Mith, This summer I bought an early (1979?) 3-point backhoe made by a US manufacturer for Kubota. This was before Kubota was installing their own hoes. The model is Kubota K-650. It works great, and does everything I had hoped it would do.
This K650 has a couple of features that I think make it smaller and lighter, for use on a light tractor:
1) The boom swing is driven by chains around sprockets with the ends of the chain pushed by a hydraulic cylinder. I think this is to make the whole thing shorter front to back, making it easier for a small tractor to lift.
2) The stabilizers slide down channels, in contrast to conventional stabilizers that swing outward.
This unit has 7.5 ft reach, 6.4 ft maximum depth.
I was told it weighs 750 lbs. With its center of gravity so far back I think it's near the limit the 3-point can lift easily, and it's the only implement I have that makes the front light. This is a 24 hp Yanmar, about 1900 lbs before ballast, loader, and those oversize tires.
At this size, a 3-point mount is sufficient. One experienced dealer advised there is no way this rig can hurt the tractor - so long as I transport it gently so it doesn't applying bouncing stress during transport. After using it a while, I think my tractor could handle the next larger size 3-point hoe, or quite a bit larger with a frame mount.