I would recommend talking with Bob of Michigan Iron & Equipment. He is very familiar with these decks. I believe his take on them is that they were somewhat problematic as shipped form Kioti but he knows how to make them right.
I opted to get one for my CK20S. Mine is a rear discharge model and i've been extremely pleased with the cut quality, though this is a somewehat heavy tractor to mow with. I had some issues with the lift mechanism on mine which had been updated to the newer twin arm lift setup, the earlier ones only lifted the deck from the left side which was problematic. Now that Bob has worked out the bugs i'm very pleased with the cut quality, it does such a good job mulching leaves that I haven't had to pick them up this year. The deck is welded (not stamped) and made from 1/4" steel. EXTREMELY heavy duty, i've never seen a deck this thick before.
Installing/removing the deck isn't particularly difficult and like pilonidal said you have to lift the front of the tractor up, I use the FEL and then remove the FEL before I mow. To install / remove the deck it's ~10 min + the few minutes to add or remove the FEL. The maneuverability of the MMM is nice though I don't have experiene with a RFM. The front tires do push the grass down which makes it harder to suck up if you are going real fast, I have to imagine it would only be worse if the deck was behind the front AND rear tires.