<font color='#000080'>Hi
I have a closed circuit smb and use it often. The main advantage is that you do not have to switch regs, unwrap the long hose and rewrap it. The other advantage is that you do not have to 'hold' the smb open whilst filling, which I think makes the task less fiddly. Remember to reconnect your drysuit though! They are quite easy to use with a little practice. I use the 4.5 ft.
The disadvantages are that you would have to leave your drysuit hose on your rig for wetsuit diving. They are expensive and a simple Buddy SMB does the job at a third of the price. Oral inflation is possible but very slow.
I see no real difference between disconnecting and reconnecting a drysuit hose and switching regs, or fannying around aiming exhaust bubbles (which I wouldn't do. Its just asking for a nasty incident). As for loss of buoyancy, surely you are neutral when undergoing this, or any other task. Thats just basics.
My advice though, is to try before you buy. You are quite welcome to have a go with mine or have a demo if we are ever in the same puddle.
Kindest Regards
Andy