I think it comes down to how much u want to spend. My buddy has a sig 556 and loves it, but.. he never shoots the thing.
-Indoor ranges don't like it.
-When we go shooting his ammo cost is way higher then the rest of us when we go pistols only.
-He also got yelled at by a range officer for having a bipod on his. RO said that's an SBR if you do that. Unconfirmed if this is actually the law or not. -They're also $1200
If I wanted a pistol in rifle caliber I'd probably get a Draco AK pistol for around $450 and shoot dirt cheap tula ammo from walmart ($3 a box). This kind of gun seems like a novelty to me. Cool, flashy, your going to get a lot of compliments on it. How often are you going to use it, and for what function?