1. The bolt stops are vastly different.

2. The Magpul BAD is a gimmick that you'll be finding a way to remove before Day 2 of a three day professional carbine course. There's a reason the bolt stop has a big pad on top, just slap it with the heel of your hand regardless of wearing gloves or not. Or retract the charging handle and release. Both are gross motor skills.

It's entirely possible that there are now more useless gimmicks for the M16/AR15 -- all marketed as "tactical," of course -- than there ever were for the M1911... Why are they made? Simply because guys will buy them. It's all about marketing, not utility.

-- Chuck