If you ever have the call for mowing anything except nearly scalping turf, avoid flails like the plague. They do a pitiful job if you try to cut "long"..... They require much more power per ft in dense grass. They're useless in wet grass. And flails equipped to do rough cutting aren't worth the time of day as a finish mower (and vice versa) Not such a glowing report from a mower that will cost several times as much as a more durable, more versitile rotary cutter.
For the record, I own a commercial mowing business, which mows (literally) thousands of acres per season. I've used some of the most expensive, highest quality flails in the business. I had plans of marketing that portion of my business as "an advantage".....Gave up on that idea real quick once I found out the added cost, lower productivity, higher maintenance cost, MUCH higher initial cost, and in most cases mediocre performance would have made my business uncompetitive.
If you have endless hours of spare time on your hands, aren't interested in quality of your work, have plenty of money laying around with nothing else to do with it, plan on mowing on an intense schedule, and just LOVE spending your time S.L.O.W.L.Y. mowing what could be done better in less time with a good rotary cutter, by all means....buy a flail mower. BUT....If money IS an object....IF time is a valuable commodity.....and being able to buy one LESS EXPENSIVE mower that does the job seems like a more intelligent solution to your needs, buy a GOOD rotary mower.
Can (and WILL) furnish you with MUCH more (detailed) facts on ground speeds in various condition/hp required in various conditions/cost (flail vs rotary) of routine maintenence per operating hour upon request. There's a perfectly good reason why over 95% of commercial mowing is done with rotary mowers (vs flails)......When practicality and common sense are factored in on the decision, the choice is simple....