I have the DMM-60 mid-mount side discharge 60" deck.
My CK-20 replaced my Toro wheel horse 315 classic tractor w/ 42" side discharge deck.
My buddy has a craftsman 42" lawn tractor w/ 2 bladed deck.
I always thought the Toro did a more even and nicer cut than the craftsman mainly since it's a 3 bladed deck w/ high blade velocity.
I also think the CK-20 w/ DMM-60 does a nicer job than my old toro and a much better job than a craftsman.
I like the MMM because when I mow w/ the loader on, the whole machine isn't ridiculously long and I can get into and around things and only have to worry about the loader clearing things. I will be taking the loader off soon to help reduce weight.
Some guys worry about weight -- I have loaded tires, so a 3000lb mowing setup could compress the soil. I haven't noticed any problems and I'm pretty fussy about my lawn (looks like a golf course).
I do plan to get an aerator -- that will help address any soil compression problems.
I'm very happy w/ my setup. I would not want to go back to my toro machine.
Deck removal is quite easy too, no tools required -- just lower it all the way down, quick disconnect the drive shaft, pull 6 pins and yank the deck out from under. It's heavy, but not too bad. It helps to have the loader on to pick up the front of the machine for easier deck removal clearance from the front tires.
My profile has a picture of my setup.
I may get some weight for the front if I end up doing wheelies w/ loaded tires and no loader on the front to balance. Haven't tried mowing w/ no loader yet.
If you have more of a yard setup like me (1.1 acre) as opposed to a field, I think the MMM is the way to go. I can get nice and close to the house, around trees, etc w/ the deck sticking out beyond the tractor width. No need to back into areas to cut close -- I think that would be awkward w/o an MMM.
Best of luck in your search.