Matt,
I never heard of a belt reel, but I have made a self-inflating buoy system that is attached to a weight belt with velcro and spandex wrap. It uses a CO2 cartridge for inflation. There is a rope attached to the float and to the lever that breaks the seal of the CO2 cartridge so the seal breaks first. The idea is that it breaks away from the belt with the pull of rope and the inflation of the bag. This could happen either by pulling the rope myself or by the fish if it yanked the gun out of my hand.
It looks pretty good, but I haven’t been able to test it yet. I have worn it a few times, but I only had 1 CO2 cartridge, others were on order, and I didn’t want to waste it on a trial. I am waiting to post pictures of it after I have tested it.
The first concern, as always is safety. If the reel is attached to a belt, then your only way out is to release the belt. Entanglement of the line with yourself is another concern. A knife would be essential.
Getting the reel in a position to be able to reel it and being able to keep it there would be another thing I would think about. With it so close to the body, it seems like it would be easy for the body to obstruct the reeling action while you are trying to keep it’s face pointed toward the fish. Maybe mount it on something like a small rod that one end breaks away from the belt. It would be like fishing with a small pole.
Let us know if your belt reel idea goes anywhere.
Don