i have a 6' brush hog and mow pastures with it - yes, it sticks out a mile.
when I mow brush/saplings under trees and the edge of the woods I back in - the 8' distance is a good thing. cuts forward or reverse, no matter.
I have a flail on order, did a ton of research - EVERY manufacturers says forward only. The all have a big roller on the back/bottom that runs on the ground and backing up it's the first thing to hit anything...maybe on a big expensive flail it's gonna be fine, but on the 'affordable' options it'd be way to easy to bend it and not realize it when backing into brush/trees/stumps/rocks, etc.
and there are 2 different blade types for flails - hammer/duck food, 2lb each and the cutting edge looks like an axe head - for brush and such. And 'grass' or 'y' blades, thinner metal and they hang down like the letter Y upside down, better for grass.
I ordered my flail with hydraulic offset - using the rear remotes it can be 'slid' on rails sideways about 20" left and right - so it can be centered behind the tractor or moved out to one side - nice for fences, over top of ditches/embankments, under tree limbs, etc.
They also make 'ditch and bank' flails - very tempted to get one of those!