AR pistols allow you to have full-power cartridges in easily transportable, high-capacity packages. They're a particularly good solution whenever ease of storage or the need to carry a smaller firearm take priority over accuracy and velocity. Common examples are for car/truck guns, bedside use and backpacking or camping. I typically incorporate a brace on the receiver extension to help stabilize my pistols but the configuration is up to you, so long as it meets the legal definition of a pistol. Caliber choices pretty much run the gamut like my other AR platforms.
All Citizen Arms pistols are built individually, fully customized, accurized, tuned, broken in, with the same guarantee as my long guns.