I know its function is that you can release the bolt without having to do so with your left hand but here's my point. The bolt locks back because of an empty magazine, so you would have to take your left hand out of battery anyway to release it and put a fresh one in. So your left hand is already out of place. It's no more advantageous to release the bolt with your left thumb while reloading than it is to release it with your right index. Unless I'm missing something?