For me, the RFM was half the cost of the MMM setup, especially because my tractor has as an OPTION, the mid Pto.
Also, to do ground engaging work, the MMM might need to come off, for ground clearance/potential damage. Whereas, the RFM serves double duty as rear
ballast...no need to take it off.
There are pros and cons in the actual mowing...
In tight spaces, as someone else pointed out, the MMM makes mowing around trees easier, and may require less sideways seating to observe the RFM in the back.
But the RFM rear discharge leaves no "trails" of fresh cut grass. And if u have an area that u can't mow right along side, the RFM allows precision backing into a tight area....if u back right up to something with the MMM, u would have a few feet that it wouldn't cut.