I have never used a bobtach style hoe that you speak of, but i do own an old beat up backhoe attachment that works quite well. The proper one allows you to dump the bucket to one side easily unlike the other style that you need to turn the machine to dump. Especially if you dig a trench then decide its not deep enough, you simply will not be able to dump the bucket without falling into the trench.
If you are doing work around your yard it will do but you will be kidding your self if you try to use one commercially i'm afraid. The “real” ones can reach further, dig deeper easy to dump.
I'd say for limited use for shallow trenches on firm soil they would be ok.
However, expect 4 to 5 feet deep instead of 9.
On soft muddy ground you will tear the soil up or may get stuck because you have to constantly turn the loader to dump the bucket. Some of the bobtach hoes have a swing cylinder in the boom to reduce skidding the loader, at a higher price of course.
Finally, using your bucket dump cylinders to press the hoe bucket into the ground puts an extreme amount of force on your quick attach locking pins. The QA was designed to be loaded from the top down, not lifted on from the bottom up. Some have had trouble ripping the lower holes out of the QA plate on the bobtach hoe iteself to.
It is not near as good as a real backhoe, but cost and amount of use (or lack of) make it a ok option for some, just like those of us with a real backhoe, quickly realize how nice a Mini Excavator would be. But we all have budgets to live within to. My personal feeling in good used real backhoes can be found for not much more then the cost of a new bobtach hoe.