As a new backhoe purchaser, this is something that caught my eye also. There are basically two kinds of backhoe attachments. One kind hooks up to the 3 point hitch on the back of the tractor, the other has a "subframe" permanently added to the tractor to carry the backhoe.
A backhoe is designed to push, pull, rip, dig and do other violent things to the ground and objects, with thousands of pounds of force. It has to have something to lean against to give it some leverage when doing this. If the tractor is the backstop, it better be a really heavy unit, like an actual backhoe.
Next best are the subframe backhoe attachments, which take all the stress off the tractor itself.
The 3 point backhoes are lighter-duty units for part-time use. Some of those are good, well-designed for that purpose, but none are intended to do really heavy work.
You can figure out the rest. Someone with a 3 point unit tries to level Mt. McKinley with it and ends up breaking something.