I have an IM 4 ft brush cutter that I use on steep pond banks, as well as some brush cutting around the place here. I bought it used from a neighbor down the road and put new blades on the thing. I like it personally. You might do a internet search for the places for parts.
They seem to be pretty well built and I don't know how old this thing is that I have. But have hit some pretty big rock with it and it has not seemed to do any damage other than dull the blades a bit. The reason I use it on the pond banks is because I don't want a lot of weight pushing the tractor around, even though my tractor will handle a five or six foot cutter.