I have a few CO2 replicas. Well, more than a few if I'm honest! I also have the real steel versions of some of them and I enjoy shooting them all. The CO2 are fun for the garden and the powder burners are fun at the range.
You would be surprised just how realistic some reps are though...

Glock 1

Glock 2

Luger P08 1

Luger P08 2