<snip> Any experience with the walk behind brush cutters?
I have a Goldoni (Italian, similar to (but not interchangeable with) BCS) 2 wheel tractor with a sicklebar and a rotary lawn mower.
The sicklebar is awesome when wading into dense briars. On one occasion when I did so the bar just passed under 16" spherical boulders. A sickle bar makes only one cut and uses little energy (old haying machines were horse-drawn, ground driven) so it will cut (most) anything that fits between the teeth and chew down 2" saplings. It will not cut a steel fence post and will break teeth on heavy gauge wire. The problem with one-cut is that you still have to deal with the slash.
The lawn mower has a 2' long, 3/8" thick, rotary blade. Putting 10 hp into a 2' swath, it will chew up anything it can push down. When I entered "unknown" brush I found a stump that broke the shear-bolt-like clutch on the mower shaft. Goldoni also marketed a "brush cutter" that had a 2' diameter, semi-shrouded, horizontal, toothed blade not unlike what I remember in old Gravely brochures.
The problem with front attachments on Italian 2-wheel tractors is that, when the front attachment is mounted, the engine is low, and the ground clearance is very limited. Uneven ground or even the hole left by a displaced cobble may hang the machine up. My machine has a reverse gear and separate dog clutches for each wheel. I have never had to winch it unstuck, but I have had wrestling matches with it.
Captain Dirty
PS. I have used a bicycle-handlebar type of brush cutter with a saw blade, and with my rocky land, promptly "cupped" the blade by bending all the downward set teeth upwards.