No, you are not kicking sand at anybody about this; they are better than a rotary brush cutter; granted I am a flailmower and formula one snob and marvel at how the five acres looks again today with no wheel marks and nice ribbons and turf that is not stressed by a rotary mower.
The flail mower has more total cutting edge surface than a brush mower or finish mower which only has a limited amount of cutting edge over 1, 2,3, or more blades.
You can buy a heavy brush mower with hammer or cup knives and have a great patch of ground after cutting.
The flail mowers entire width is cutting at all times while operating at 540 PTO speed and high power.
The thing is the flail mowers rotor is traveling at 100 miles per hour or faster swinging all the knife blades SLICING just a tiny bit of material while moving forward with a reverse or forward rotor rotation.
The slower you travel and the more grass knives you have the finer the clippings and this applies to brush as well as it will knock your weeds down the ground--you may have to go over the thicker stems with the flail mower raised and lowered a second time at a lower cutting height but that will destroy the stems quickly.
You can mow slowly in a spiral and shred everything down to the ground with no issues and mow nice turf after you mow brush if you have grass knives.