Engram Flush, like Slot Machine, is a cheap to rez but taxing to break code gate with unassuming subroutines. Slot Machine is great, and I'll compare Engram Flush to it to get some sense of how good this new code gate is. Incidentally, both reveal runner cards, and thus can give Hyoubu Institute a credit.

2 for a strength 5 code gate with two subroutines is a fantastic deal if the runner breaks those subroutines. If they don't, they're liable to lose a card or two provided you have a read or knowledge on what they're holding, which you're likely to have in Hyoubu or Chronos Protocol. You can hunt down any I've Had Worse the runner might be holding for your damaging ice by naming Event, and in general the ability to pluck chosen cards out of the runner's grip is already what Chronos Protocol decks are going for.

Both Engram Flush and Slot Machine are somewhat liable to misfire and won't always be as powerful. In Slot Machine's case, it depends on the top cards of the runner's stack, but at minimum you will cost the runner 3 even if their stack is empty or they blank its encounter effect. Engram Flush on the other hand can be walked through with an empty grip, although that's probably a bad idea against Jinteki. Engram Flush will also do almost nothing against Hunting Grounds or if you just name the wrong type with the encounter effect, which the runner will know before they choose to break or not.

I think you probably have to really be taking advantage having existing knowledge of the runner's grip to make Engram Flush good enough. It's less reliable than Slot Machine, although it is a whole credit cheaper which is a big deal at such a low cost. My prediction is that this card is good enough for Hyoubu Institute and Chronos Protocol, and maybe Harishchandra Ent. at a push, but its going to be a tough sell for any other corp.