Rainer, I purchased two of the scubatoys model for my wife and I. (
http://scubatoys.com/store/Scuba_Acc_signal.asp first one that says all the DM's in the carrabian are using them)...
I have never actually used one yet thought

I'll have to try it out in my pool this weekend...
What I liked about it, is the way the straps are sewn on with the clips. This arrangement allows it to function as a lift bag, I'm not at home but I belive the material's that came with it said it had a max lift of nearly 10 to 25 lbs. When I get home I'll hunt around for the paper that came with them (I save everything scuba related) and let you know for sure, but they do seem sturdy enough to support 20 or 25 lbs easily.
They are a bit bulky, and although WILL fit into a BC pocket, My wife and I have Aqualung Passport's (the kind that fold up into thier own built in carry bag), and once you get this plus a small spool (I purchased the finger spools from scubatoys) there really isn't room in your pocket for anything else.
Instead I'm trying to figure out a way to clip them off on our backs (perhaps add a D ring to the tank band?) so that we could just reach back and unclip, or simply grab my wife's off her back.
I plan to ask our instructor when we do AOW if he has time to show us how to "shoot a bag", we will probly do search and recovery as one of the dives.