I have an older john deere 5fter on my lx2610 which is 25hp. Some members were saying it was too big and heavy for my Kubota. I used it to cut marsh grass and cat tails,plan on corn stalks next spring. I start out in an open area, have the rear of the mower tilted up, in L, and have the front loader on. I creep along making sure it chops everything up nice and I don't come across any obstacles. Only once did I have an issue bogging down. With a 5ft mower it's as wide as my tractor but I'm running over what I want to mow. Some guys get a 4ft to straddle what they need to mow. I just mow a 10 foot trail that takes 15 minutes so speed is no factor for me. If you have a large area and have a heavy foot something smaller like a 4ft would probably be best. On hunting forums I see alot of pictures and videos of guys using brush hogs as bull dozers trying to mow down 6 inch diameter trees........then they wonder why their stuff isn't working.
Do you have a quick hitch on your Kubota? If so you'll need this adapter to let the mower float.