I suggested the Manta reel over the spool because the Manta locks bag down once you take pressure off the handle. No messing with double enders mechanisms which require 2 handed operation. Even though a plastic spool WILL just spin in front of you until the bag hits the surface.
As to winding up while surfacing, you just may not be able to do it. The reel might need to hang while you follow the line to the surface and retrieve the reel and line once you are back on the boat.. I know from your other thread, you were speaking of shooting from 30 ft or less.
The point about oral inflation challenges is a good one. Since you are diving a 7ft hose and necklaced 2nd stage, be certain you are able grab your alternate without using your hand. Even then, with the long hose routed properly behind your neck, it should hang nicely in front of you on your chest when out of your mouth. Another thing to think about to, if you remove the reg from your mouth and let it hang (or clip it off), you may have to adjust it to avoid free flow.
The AP Valve bag is the one I was thinking of earlier.