I have a B7800 and it handles my 5 foot John Deere medium duty rotary cutter just fine. I just got through brush hogging some overgrown briars, saplings, and vines a couple of days ago. The B7800 with FEL and the rotary cutter is a good combination for clean up work. I've never used a flail cutter, so I can't comment on them.
Now, if the B7800 just had position control!
Now, if the B7800 just had position control!