Do these use standard lead shot pouches as weights?
The system is 2 parts: a 'holder' with a stiff clip (portrayed on the left) that attaches to you belt and a 'pocket' (portrayed on the right) where the weights actually go. When you want to release your weights, you unclip the (VERY) stiff clip, pull the pocket out and drop it...You can load the pocket with lead pouches or with solid weights. Lead pouches will conform to the shape of the pouch more easily.
BTW I use this system for technical diving (twin tanks and rebreather). Technical divers typically never consider dropping their weights as deco would be missed. I feel that a recreational diver in difficulty would find it very difficult to release the VERY STIFF clip in an emergency situation. YMMV.