If you've never fired a pistol AR, you should. They are a lot of fun!
I've been an AR carbine guy for a while until someone at the range let me shoot his pistol AR. those things are pretty cool IMO, and offer the practicality of having a rifle caliber in a compact configuration without having to deal with legal issues (NFA). Of course, the downsides are the huge muzzle flash and decreased bullet velocity. In some states that do not allow short-barrel rifles (SBR's), the pistol AR is the only legal way to have a short barrel firearm that fires rifle rounds.
For legal reasons you should never mix-n-match rifle length AR's with pistol AR's. No one is stopping you of course, but if you do then you are breaking the law!