I owned a gen 1 in .45acp...it jammed every other mag no matter what "premium" ammo i ran. was using glock factory mags. it was fun as hell, but very frustrating. sold it.
I almost bought one when they first came out. After handling it and seeing how heavy it was, I passed. A good friend bought and sold one. He never got it to run without a malfunction. I felt like I dodged a bullet on that one! Now there are a ton of great alternatives out there.
I’d go 9mm. I’ve been looking at them for a while but haven’t owned one yet. It’s such a novelty gun that I’d want the cheapest round to shoot through it.