I am a longtime vocal critic of small back hoes in general. And I have a Great Bend unit for a Kubota
B2910 (30hp) tractor so I think I have some basis for my opinions.
First, let me state that a 3pt back hoe is going to typically put more stress on the rear of the tractor than a sub-frame mounted back hoe. If you get a BH, get a sub frame mount, you may lose a bit of ground clearance but you won't likely break the rear off your tractor. Also, most of the 3pt mount units I looked at had lower capacities than most of the sub-frame mount units.
Second, let me state that if you have specific needs for a backhoe on a very regualr basis, then a backhoe on the rear of your tractor might make a lot of sense.
However, if you are thinking of doing serious work with a backhoe like digging a new septic field, foundation, etc, then you are probably in way over your head with these little things UNLESS YOU BUY A BIG ONE and put it on a LARGE TRACTOR. So for my opinions, let me state they apply to a typical BH that would mount to a typical tractor of perhaps 35hp or less.
Compared to renting a track hoe for under $200 (36 hour rental including delivery & pick up)
Thomas Track Hoe/mini-excavator the back hoe on your tractor will have FAR LESS ability, reach & capacity. Further, it will not work nearly as well in tight spaces as the overall length of a tractor with FEL and BH is going to prevent you from EFFICIENTLY getting into places. I had to dig along the side of my pool last year, on one side of me was the pool, the other side was a wooded hillside. The space between the two is only about 15'. The Kubota
B2910 TLB is longer than 15'. Of that 15' that was available, I had to dig out a 4' wide area so there was about 11' available to work in and that included the area where I had to pile up the spoils. I was able to dig a 40' to 45' long trench, 4' to 5' deep, 4' to 5' wide with the track hoe in about 3 hours. My neighbor, who is far more experienced with a TLB showed up the next day to look at the project and estimated that it would have taken 2 to 3 weekends to do the same job with the Kubota/Great Bend combo due to reduced reach, reduced bucket size, having to transport the spoils to another area so I could maneuver the TLB, etc.
I think if you have some real jobs, you MIGHT be better off to line them up, rent a small track hoe, and knock the jobs off in a weekend. You'd likely save yourself $6,000 to $8,000 and save a lot of time.
IF you have a lot of small projects, then a BH on your tractor might make sense. But I could pull some might big stumps very quickly with a rented track hoe, while I read about people taking 2 to 3 hours to pull a modest size stump with a small TLB.