I've fired the FiveSeven. My friend has two and brings them to the club quite a bit. I've even bought ammo to shoot in his guns.
I haven't found the ammo to be that expensive. Certainly no more so that 50 rounds of decent quality .45 ammo. It's harder to find than it is expensive.
The FiveSeven is a bizarre gun. It feels big. The controls are a bit hard for me to manipulate. And despite its expense, it feels very plasticy. Even the controls are plastic. Frankly, I think it feels rather "cheap."
The gun is fun to shoot. It doesn't recoil that much, but for some reason it has a helluva muzzle blast. It's loud and you can definitely feel it go off when you are next to it.
I like the gun, but only enough that I would buy ammo for someone elese's gun to shoot. The FiveSeven isn't even on my radar as a future purchase. It's a novelty IMHO.
I don't see it as a real good concealed carry gun. It's big, fat, and his high sights. If this is your first handgun, or you want something to carry concealed, I'd recommend something else. If you want an interesting piece to show friends, or just want one for no particular reason, by all means, buy one.
Even though the gun has some notoriety as the Ft. Hood gun, I'm not convinced it would be the best choice as a self defense gun.