I just tried my Endine today for the first time. Middy carbine. Recoil is...... different. I'm not entirely sold on it yet. I had an H buffer in it before. Just a couple of times it didn't lock back on empty, although I don't have a problem locking the bolt back manually.
Contrary to what others report, I saw the most difference shooting off the top of one of my (full) ammo cans. I push the foregrip (which is out front) against the can; previously, the AR would jump back from the can on every shot. Now, it stays virtually still.
Felt recoil is reduced. Offhand, the barrel jumps less (better than my 20" A2) - I'd say the Eotech reticle jumps up about 10 - 12" at 50 yards, just for an instant - and it seems to come back down on target much more consistently.
I'll have to play with it more, and I also want to see what it does when it isn't 25 degrees outside. I would also like to try the MGI buffer at some point.