Keep in mind that I live in California. Two simple purposes...
1. In California, an AR pistol is the closest thing I can get to any kind of SBR. That's the way it is here.
I am building one with an 11" barrel and the OAL will be >26". This means that I an legally add a VFG. So I will have four points of contact, handgrip, VFG, cheek weld on the foam covering the buffer tube and a single point sling. With four points of contact and bracing, you can actually shoot fairly accurately, much better than an AR "pistol".
Overall, it is a range toy, it is for fun, not for competitive shooting or HD.
2. In this ridiculous state, an AR pistol is a political statement. Is it practical? Not really. Is it easy to shoot well? No. Is it fun? Yes, they are. But best of all, the anti-gun forces that run Sacramento don't want me to have one of these. In California, our off-list AR type rifles are considered to have "evil" features so an AR pistol is even more "evil".
Same with my Uzi. The original IMI Uzi is a banned AW here, so I have a Vector. Granted, it is a neutered 16" barrel, permanently stocked, semi-auto version, that is all we are permitted here so that is what I have. I plan on obtaining an AOW for the same reason. I have these guns because I can, because it is an irritant to the powers that be. None of the three weapons are highly practical and I have practical guns as well.
It must be hard to understand if you live in a free state but here, that is the way things are here. AR pistols are kind of cool, they are fun to shoot and they are interesting to build. They definitely serve a purpose, especially here in California.
BTW, Franklin Arms in California makes an AR pistol in .450 BM, that thing is crazy. Makes a 5.56 AR seem "normal" so it is all relative.