There is no free lunch with mowers. Rotary cutters are the most rugged, and they have an acceptable cut. Flails have a better cut, but they have some significant limitations: their maximum cut height is often very limited (the one referenced above cannot go higher than 4 inches/ rotary cutters typically top out at 10 inches), they cannot be lowered into a thick area of bushes/briars to top it to reveal what is underneath before committing to a closer cut (briar patches on farm land often conceal stumps, a pile of rocks that were removed from the field or something that caused the area not to be mowed) and flails can suck up rocks and sticks that jam the mower (a multi-hour problem even if you have the parts/belts you need). Finish mowers have the best cut (on low height grass - not good on high grass), but they are the least capable of handling foreign objects and brush.
If I could have only one mower, it would be a rotary cutter. I have two mowers (rotary and finish), and I am happy with my choice. However, I might have been just as pleased with a rotary and flail combination if the land did not have so many rocks. In the first reclaimed field, I regularly mow at 5 inches with the finish mower to help the grass grow thick and avoid any remaining rocks.
Messick's has a good video about the pros and cons of a flail (complete with a jammed stick).