American Rifleman reviewed SIG's Enhanced ACP platform that turns pistol in to carbines. Out of 3 models(Standard, Enhanced, LE), they looked at Enhanced, which comes with SIG SAUER Mini Red Dot Sight, a quick detachable sling swivel, and a single point bungee sling.
Because it comes with a sling and not a buttstock it is not subjected to federal law. Shooter should use tension of sling to get better accuracy.
American Rifleman noted that the platform allows more options for shooting, but also noted some shortcomings like charging handle being heavy.
From: American Rifleman