I would fully agree with both from what I have seen and heard. I will add that I am still in the research phase, however if I was able to pull the trigger today, I would be handing my $$ over for the flail, even while the brand I will choose is still being researched.
Another important item to note is that while I still do not doubt that deals can be had on both sides; to me, even if I could get the same quality rotary and finish mower for the price of the flail, that still makes my case for getting a flail...
Let me explain. On my new property I would have the need for both, brush(bush)'ing about and mowing many acres of each. With the flail, I don't have to change impliments going between the two. So if I need to do some lawn and brush on the same day, I would just plan to keep the flail on. If I had both bush and finish mowers, I not only have to change them to get the same result, I also have to store 2 impliments of a much larger size.
You case may vary, and what you choose to do should relate only to what you need and how they will be used. They both can get the job done, IT has show very good pro vs con, and the good news is either choice gets you more seat time.
The final 'nail' in the case for me what the new property that I am moving to has a very large area of the home facing into the back yard; with both floors having full glass exposure from the floor to the top of the second story celing.
Yeah, replacing even 1 window would be much of the cost of a very nice flail.
Good Luck.