Fair point JP, but the reason I choose unlimited ammo is to help you get your deflection aiming better and sooner. When I trained, I'd pick a spot in front of the target and start firing. If I saw no hits land, I'd keep the trigger down and pull back and give more lead. When I saw the hits land I'd make a mental note where I was aiming.
If you try that with limited ammo, you'd be reloading the QMB mission every 5 mins and would lose 'your flow'.
Horses for courses...
p.s. I forgot to mention, it helps if you have Wonder-Woman view on. So you can see your rounds hit below your gunsight.