Okay, most people underrated this ice by quite a bit. While it doesn't belong in every NBN deck, it's powerful in the decks it does.
First of all, this facecheck is brutal as hell. It's somewhat surprising, given that NBN decks haven't had affordable painful sentries for a while. If you run into this without a killer, say you're feeling adventurous turn 2, you're getting blasted. It turns out that 2 tags is actually a lot--who would have known--and if the corp is playing R+, they get refunded 2c.
This is not to downplay that a tagless runner with basic breakers gets through this for cheap, but if NBN is playing fast, you're not always going to have your killer, and that means you're in for a world of hurt.
Where this gets absolutely terrifying is with the armada of tag cards that NBNs, and especially R+ decks, pack and fire at you en masse. Oppo Research is the main toy that R+ is packing. It can be very tempting to go tagme when faced with Funhouses. I've even seen Amaze get played these days. What's important about Starlit Knight is that you CANNOT IGNORE THIS MASS OF TAGS, or the server its on is locked down. It's much more powerful than Resistor for this purpose. There's ways through Resistor (most notably just beating the trace), but its hard to ever get through a Starlit Knight that's amassed 10 subs from you going tagme through Funhouse and then slapped with the Market Forces. Not that you even need to get hit with the Market Forces, to be honest, it's hard enough to get through at that point.
There's basically two things that a deck needs to be able to play Starlit Knight. First, you need to be playing fast enough to pressure the runner into either floating tags or facechecking into it. Second, you need some way of consistently landing and forcing a large number of tags to make its effect relevant.
You usually see Starlit Knight out of R+ and wide decks with ARES, but even if they're not on ARES, it's normal for the corp to pack Oppos and Funhouses and call it as enough to play Starlit Knight. All in all, be very careful about going tagme against NBN. It's not like in the days of Boom, where even if you were about to die you could desperately search centrals to either deny the flatline or win outright. If there's a Starlight Knight on R&D, you're typically as good as dead.
I'm not even sure I'd say tags are less dangerous at this point. If you float tags trying to steal an agenda and get hit by Market Forces, or just get Oppo'd while poor, this ICE can leave you with essentially no real option to win. It's definitely one of the first ICE you should be considering in R+.