Um. The HTC One MIGHT be similar, since its similar screen size i think BUT its not flat on the back, its actually curved.
so the HTC First is UNIQUE yey haha. I got my awsome case for like 2 bucks off cellphoneshop.net
its clear and 2 piece and doesnt come off when the phone is dropped and it is quite thick so it protects the phone really really well.
Getting a case meant for another phone is basically throwing money away. And when you drop your phone and the phone just falls out of the case, you'll be throwing the phone away too. There is quite a selection of good cases online. What's wrong with amazon/ebay?
My main purpose of buying the case is to add width to the phone. As it is, it's just a but uncomfortable holding the First because of the small bezel size.
Also I don't have a credit card so I can't buy online :/