I just received my Magpul M-lok QD mount today, and I have to say I'm impressed. It is VERY small, super lightweight (feels like nothing is even in your hand), mounts up solid, and (gasp) is rotation limited. Very nice piece. I ordered one because I'm less than impressed with my "built in" ALG M-lok 13" FF rail's QD (no support as it's not a "socket", will rotate if pressure is put on, and quite honestly, I wouldn't trust that QD hole for even casual use. It's worthless and I'm not sure why ALG even bothered to put the hole there).
Back to the MP mount.... it mounts into a single M-lok slot, so it can be mounted far forward (which I prefer). I DO wish it was melonited steel (as some of their other products), but instead it's aluminum. I guess that's a blessing and a curse. As said, being aluminum, and tiny, it is ULTRA light weight. How strong it is only time will tell, but it is a good socket with substantial surround, so I'll have faith in it unless proven otherwise. And for $19 shipped (Aim Surplus).... well done Magpul!