Alright, young Shaper, let's talk decoders.

If you're looking for a main breaker, there's really four main options: ZU.13 Key Master, Gordian Blade, Torch, and the new Study Guide. There's also Refractor, Yog.0, and Cyber-Cypher but those all need specific support to be useful, so let's just look at the three standard decoders for now.

If you're debating between ZU, Gordian Blade, and Torch, the real question is, how big is the ICE you plan to break? If you expect to mostly be staring down Quandary and Enigma, then Zu will do the job at nearly same cost as the more expensive breakers and for a helluva lot less up front. On the other hand, if you plan to be hitting the same Lotus Field over and over, you'll be glad you paid extra for the big grandaddy Torch.

This is more important the more times you are going to be running. If you're breaking a Lotus Field, it will cost you 4 per run using ZU, and only 1 per run using Torch. But you paid an extra 8 to play the Torch in the first place, so you need to make at least 3 runs for the initial investment in the Torch to pay out.

The problem is that you have to decide which breaker you want to build your rig around before you ever see your first piece of ICE. Opting for ZU means you can get set up and run faster, but means that big code gates like Tollbooth or Wormhole basically shut you down. Torch gives you the power to burn through any ICE...eventually, and that means the corp has lots of time to set their own board up.

But then there's Study Guide. Where the three other decoders are essentially small/medium/large, Study Guide is one-size-fits-all. If you're facing down weak code gates, then you only need to charge it up a little bit to have a breaker that is strong enough to handle them. On the other hand, if you're looking at monster ICE, you can make SG an even bigger monster. You never get caught in the embarrassing situation of having to break a Quandary with a Torch, or a Checkpoint with a ZU.13 Key Master.

There is a price to this flexibility, though. Yes, Study Guide can be a weak breaker, but it costs 2 more to install than Zu. Yes, Study Guide can be a strong breaker, but it costs a total of 11 to install and get it to four strength, two higher than the 9 it would cost to install Torch. And even though you can break a Wormhole for 1 after boosting it to strength, it's going to cost you a staggering 17 to get there first, with the saving grace that you don't need to do it all at once. Study Guide is jack of all trades, and a master at none.

Of course, this is all talking to Shapers. Anarchs and Criminals are probably going to give Torch and Study Guide a pass; four influence a card is a lot to ask, especially when ZU is only two.

Kit always deserves special mention when it comes to decoders, and in this case I think she's really happy. Kit's greatest strength is early-game aggression: being able to hit any single-iced server is terrifying for the corp until they manage to double-ice their centrals and scoring remote. But she also needs an efficient code gate breaker, to deal with high-strength sentries and barriers turned into code gates from her ability. Study Guide is the only decoder that fills both the early rush need and the later power-breaker need.

I tried to make this program work for last three months of playtesting and finaly I had to give up and go back to good old Gordian Blade. Here's why:

In a land of Fairchild 3.0, DNA Tracker and Mausolus, or even good old Tollbooth and Archangel, Study Guide sells you fantasy about having to pay only once to pump, and then come back next time for jest one or three credits.

This works only when you are playing against really slow corps. But nowadays, ETF will try to rush you behind Fairchild and Ravana 1.0, and versus NBN dumping 15-20 creds to break that first Tollbooth willl swing tempo so much in corps favour, that you will have as much power tokens on Study Guide as tags on your head.

You must be fast or go home. Gordian will still help you against stack of code gates, and will give you chance to snipe that Astro or Breaking News behind pesky early Booth. I play very "controlly" builds, with Magnum Opus. I'll have money late game, but I must survive till then. In many cases Study Guide was just too slow.

K, first off I would like to say that @tiedyedvortex review is excellent, but I would like to narrow it down it a bit more after my experience playing this with Rielle "Kit" Peddler: Transhuman. First off, we all now Kit is about early aggression in order to make most of her ability. IMO this gives you 3 options: Gordian Blade, Refractor and Study Guide. You also have Torch and Yog.0, but these builds require more specific combinations in card draw (Test Run+Scavenge or Dinosaurus+Scavenge etc) and those builds are more suited for the late game.

Now for the first 3: Gordian Blade is the most aggressive. You install it and you can run with no problems right away. The downside though is that Gordian Blade has the worst late game sustain and boosting it with recurring credits is less efficient as with Refractor. This is a bridge you have to gap while building your deck.

Refractor is cheap to install massively efficient with it's recurring credits, has great sustain, but requires stealth credits to work. With 3x Cloak, 3x Lockpick and 0-3x Ghost Runner it shouldn't be to hard to see a stealth card early. You are devoting quite a large portion of your deck to make it work, can probably make only one run a turn in the early game, but it leaves you a lot of real credits left to do other stuff. Once you go late game it really starts to pay off.

Study Guide fits in between the two. It gives you early game independence from other cards like Gordian Blade (although a lot more expensive), but once you slot in the right support cards it gives great late game sustain. The cards I'm talking about is Stimhack and Lockpick or Cyberfeeder (you can also use Cloak, but then you need support). Installing Study Guide and then using Stimhack gives you a permanent S3 decoder right of the bat, same S as Yog.0, which is absolutely fine for most early game ICE. Once you get your Lockpick out you can let it grow on recurring credits each turn (even if you don't make a run) or just pay up front. I've had games in which it was S5 by turn 3, making Tollbooth a joke for the rest of the game. Another bit advantage IMO is the fact it doesn't need recurring credits each time you run, so you are perfectly able to make multiple runs without worrying about running out of those and still be as cheap. The Lockpick you are using first to boost it, switches over to helping you break subs.

I would also like to give a special mention to Escher. A card that is nearly forgotten, but fits great in a Study Guide deck. Firing it in the mid-late game can absolutely wreck 1 or 2 servers for multiple turns. It fits Study Guide better than Refractor as it can take more advantage of it in a single turn (Esher + one or two cheap runs, before corp starts rebuilding).

Conclusion

Is Study Guide better than Refractor? IMO it is about the same power level. A Refractor deck is a deck in itself. It makes one run a turn and it does it very well. Study Guide gives you more room to play with. You can go all recurring with it (for strength boost early game, sub breaking late game) or brute force it with pure econ/Stimhack or you can do both.

If I could make a chart for strength over game time then Study Guide will have a same peak as Refractor early game, is weaker mid game and stronger late game. This makes Refractor better for fast advance, but I think Study Guide will be better for against RP or Glacier.

Study Guide is an interesting breaker that can ramp up as the game progresses, in theory. A corp will typically start by installing cheap ice until its economy can support something more expensive. This means you can throw down Study Guide and increase its strength as needed. Rielle "Kit" Peddler: Transhuman no longer has to decide between Torch and ZU.13 Key Master or Gordian Blade

In practice this isn't the case. Some of the most common early ICE are Enigma and Eli 1.0. Who wants to pay 9 credits to install and break Enigma. 13 for Eli? No thanks! Even if Study Guide is beefed up for the rest of the game, that credit hit opens a scoring window the next turn.

That being said, in combo with Personal Workshop and Stimhack, Kit can really make it shine. So is it worth one brain damage to install and boost Study Guide's strength to strength 3? I think so, if you're running Plascrete Carapace.

It can work in Nasir too if, but I don't think as well, unless your meta is full of multiples of Tollbooth and Lotus Field.

Kit loves to study, especially with Omni-drive and Lockpick acting as key supporting sources. All it takes is a good draw, or a trip to Tyson Observatory to find the citations you need. See, you can't just walk into the final exam with one power counter and hope you're going to be able to boost up to face whatever nightmare the Corp has for you. You think you can afford that with your Student Loans? With recurring credits you're essentially able to boost for free, every turn, at any time! You'd be surprised at how quickly the counters stack up. With a Paintbrush on the table (using the MU you freed up using Omni-Drive!) or Tinkering in your hand, you can easily batter through multiple layers of ICE with minimal expenditure, since an investment in Study Guide is an investment that stays there the *entire game. Of course, such a valuable investment quickly becomes a massive target, so a Sacrificial Construct can also be useful.

Honorary mention also goes to The Toolbox, which is an excellent choice of console if you want to get more out of the Hitchhiker's Guide. The issue is usually that when you have enough money to get it set up, you already have the economy you need to fund public education. However, it won't ever rotate out, unlike Lockpick (bless its tiny decoding soul).

Egret is another possible supporter for Study Guide, acting as a permanent Tinkering on a single piece of ICE. I haven't fully tested it but it seems promising if less flexible (and Scavenge can help with that, of course). Just watch out for Magnet**.

I'm not sure if I could recommend running Study Guide by itself - it's definitely a breaker that requires support. But if you give it that support and play well, it can absolutely pay off. No server is safe! No ICE is unbreakable***!

tl;dr - Study Guide is really amazing and with a little Tinkering can even be your only breaker, but Lockpick is rotating out soon and we'll have to reevaluate after that

*when playing Netrunner

**but don't actually watch out for Magnet with regards to Study Guide, it's a code gate. Study Guide eats Magnet for breakfast.

***not a guarantee