Well, the original purpose of the emergency release buckle was so that if the sling gets caught up on something, you could hit the buckle and free yourself.
If you just want to set the rifle down easily, this sucks as it leaves several feet of webbing trailing from the rifle. The MOUT solves this problem nicely.
On the other hand if somebody is grappling with you and using the sling as a handhold, or you can't get through a space because the sling is hung up on something, hitting the release buckle on the MOUT won't do anything but drop your rifle while leaving you still hung up.
Like everything else in life, it is a compromise depending on what you need to do with. Nice 3-gun sling though as it allows easy transitions and you can snap and unsnap into the sling easily.