I like it quite a bit. It seems like a good tactical weapon and you just feel like your playing in a smart stealthy way if you use it in combination with smoke grenades.
But then it would be too over powered. (Fmj also increases wall bang power) That would just be beast shooting through walls.
Yes, I used it in SnD. It only works on players that don't move, so it can be decieving if the enemy is running behind a corner. If the enemy is laying prone, just waiting for the your team to turn a corner, its great to see where he is, line up your crosshair to him, and then slighty shift into the open to quickly take him out. This worked on Slums a bunch.
You have highlighted the problem I have with the MMS. It definitely slows down your gameplay, especially if you are ADSing while advancing and looking for bad guys around the next corner.
It is a different type of attachment, and one that has some nice benefits when used correctly. When you spot that guys outline crouched behind a wall you were going to go by, it brings a smile to your face, because you know you are going to ambush the ambusher. Like some have mentioned, smoke is a friend of the MMS.
I made a class up to try out how much of a knob I could be with the MMS. PDW with MMS/Silencer, perks of choice, smoke + bouncing betty. While defending a Hard Point, you know that the enemy is going to try and swarm you eventually. Just before they would rush in, I would drop a betty and lay down the smoke before going to some sneaky vantage point and commence to ADS. I was surprised at how effective it was in some lobbies (some maps/lobbies it was pointless). Kind of nooby knobby, but it was a fun experiment.
I think it needs a little, not too much, faster sweep. it kinda sucks when it changes the pace of your game. i know it's used in a lot of SnD & HC types. if that was its intended purpose for those gametypes.
I find it pretty useless, TBH. You can't use it with FMJ, distance is too short, cycle is too slow, and it decreases accuracy?
You can tell they thought it would be more used/abused than the TF...