A B series tractor is taller and has greater clearance than a BX.
So you wouldn't say the MMM is the best implement, yet you prefer it? I must be missing something.
I have the 60" deck on a
BX2200. Before I got the brush hog, I cut the rough pasture with it. If the stuff is only 12 or so inches tall, this can work. When an inch or two taller, it will lay over like this. By the time you reach 18", mine will clog and stall. I don't know what your secret is, but your experience differs greatly from mine. As to sapplings, if they are soft material, high water content and not too stemmy, and you hit only one or two, I could see an MMM cutting it. If any more stemmy and numerous, that seems very difficult. The MMM depends upon sharp blades traveling at high speed to cut through material. Any degree of substance is going to provide resistance and slow those blades down. Much stemmy material is also going to dull the edge, requiring reshaprening prior to cutting lawn (if you want a cut that is clean as opposed to a ragged tear).
To the OP:
A rotary brush cutter does not actually "cut". It breaks material. The blades are massive and at full speed they have great inertia. The impact of this high inertia simply breaks and pulverizes whatever it hits. Furthermore, if it hits a hidden object of substantial mass/resistance, the blade will not stall the drive mechanisms and the engine. The free pivoting blades are attached with hinge bolts to a spindle pan (aka stump jumper) and when hitting something immovable, they just change angle and glance off while all of the drive mechanism continues to move at full RPM.
Under favorable conditions, an MMM or sicklebar mower CAN do a marginal job. Neither of them is going to do what a rough cutter will do, however. I mean no disrespect toward other posters. Nevertheless, I have experience cutting in the rough with all 3 types of devices. I also believe the vast majority of members here will agree with me that a rotary rough cutter is the best tool for this job. It cost less. It has a simpler design. It has fewer parts to maintain. It does the job faster. It applies the horsepower in the most efficient manner (brute strength) to simply smash and pulverize the material where it can decompose and return the nutrients to the soil without thatch which will obscure sunlight and kill the remainder of the plant below. I respect the opinion of those who disagree, yet I posit these points of logic and the number of posters who support the rotary cutter as evidence for it as the best choice.