Looks weird but way better than the 203. Little awkward for clearing rooms though. Lotta guys carry it unmounted by rigging a sling or strapping it to an assault pack.
HK likely wouldn't sell it to you, but with the correct tax stamp, it's legal to own. They're destructive devices under NFA34.
ETA: COTS refers to items already developed as sold that happen to meet the requirements. The Army didn't want to develop it in-house, or have a contract out for R&D, basically.
Ya'll have really never seen the 320. They had those in the army for a couple of years already when I first went in. You can mount like a traditional 203 or use them independently. I liked em as a m4 with a 203 was always a little much for the rifle and didn't promote accurate shots.