I have two of these and my wife uses one as well. We like ours alot, but here are a few pointers:
To get the velcro open easier I create a kind of zipper. Instead of putting the smb entirely in the bag, I leave half of the double ender attached to the SMB/Spool sticking out of the velcro closest to the back plate. This way when I want access I grab it, push down from the back plate and it opens the velcro to reach in. Nice one handed method just rember double ender near plate so you have leverage to push it open one handed.
On my single tank rig I've attached a tiny Light Monkey jump spool with 15 ft of line on it that fits nicely in the pouch along with a 6ft smb for shooting from safety stops and it works out great. Instead of trying to shoot with the tiny spool, I just clip the double ender around the line and let it's weight drop the spool to 15 ft below me, when I shoot, it comes right up into my hands.
Diving Tec/Doubles I use a bigger SMB and reel from my hip with lots of line on it.
Not all SMB are equal, some roll up tighter than others and are easier to fit in the pouch, I fit a 10ft Carter DSMB, which rolls tight, in mine with no problem although I found two things that makes deploying it a lot easier.
First I cut off the velcro strap it used to keep it closed so its velcro dosn't try to grab on the velcro at the openeing of the pouch. I added a loop of bungee to keep it tidy when not in the pouch and keep an option for just clipping it off if needed.
Second, I roll my SMB inside out so the end I inflate from is on the inside of the roll . This way I pull down on the double ender to "unzip" the pouch and when I pull on it I'm unwinding it from the inside out with little friction- looks like a chineese yo-yo. This way I am not trying to pull the entire diamater of the SMB roll with my fingers around it through the opening, just the tiny inner bit. I pull out just the first couple of feet I need so I can attach the full size reel and then pull the rest out just before I shape and shoot as normal. Same technique works just as well on the tiny reel and smaller smb.
I never try to restow in the water, but imagine it's hard to do.