I have never used a flail mower, so I cannot make any comment about them; good or bad. However, as I've mentioned before, I took exactly 1 contract mowing a highway median that began .5 miles from my house and went for 5 miles. To be polite, I lost my hind end on that job! I hit everything possible hidden in 3' tall grass it seems, including rotted deer carcasses, rocks, plenty of disgarded trash, a dang section of barb wire about 50' long and,
the worst, several "gatorbacks" (as I learned they are called), the retread part off of semi tires. Besides the potential damage to my equipment, it took 6 full hours with 2 people working to get a 'gatorback' out from under a rotary mower being pulled by a 120 hp PTO tractor!
I'm not sure we ever got a single mowing completed without issues. Litterbugs really tick me off. If you don't clean up the litter before/after you cut, it looks terrible and sometimes I wouldn't get paid until I cleaned up the mess. My contract was to mow; period. Nowhere in the contract did it say that I was the caretaker of 5 miles of median and that I would fill two dumptrucks with trash each time I mowed. God bless the guys who make a living doing such jobs! It is NOT an easy way to make a living. I won't bore anyone with the numerous stories I can tell from just one season, but it sure wasn't easy work. Unless flail mowers are extremely tough, I don't see how they would work well for cutting tall grass; especially if you don't know what you may find in that grass. Again, I've never used a flail mower, so that's just my opinion.