In the past if you lost your copy of a game your Pokemon were lost too, but with Poke Bank you can at least keep your hard trained Pokemon. Especially competetive battlers who have like hundreds of competetive Pokemon don't have to worry anymore for losing them. For this price it's pretty much a steal from the players side. The only thing I don't get is, why it costs more if you're living in Europe. Well at least the first month is free so you can at least give it a try.
I'm quite curious how the hack check will work. I'm guessing that it will be done right with the conversion, since Pokemon aren't stored in pkm files anymore, but rather pkx files. The best way for them would be to allow hacked Pokemon, but editing them so they are at least legal and add some kind of ribbon preventing them from getting traded or used in wifi battles. That allows people to keep their hacked Pokemon while preventing evil hackers from abusing the system (well at least for a while since there's never a 100% chance of absolut security; but that applys for other methods as well).
Well, we'll see.