Opinions opinions, everyone has an opinion. So Do I but I actually own and operate one of the HF ride on trenchers (like a small back hoe) and it works good for me. I have few illusions of grandeur about it being a humongous industrial rated monster digger but it trenches and digs OK for me. Like every machine it has its pluses and minuses and it takes time to learn to use it efficiently (well it didn't take me long to be productive but it takes getting used to the controls so you don't swing the arm when you meant to curl the bucket but that is the same on every machine I ever operated. One of the funniest things I ever saw was an honest to goodness true expert track hoe operator (30+ years in oil field) trying to operate an extenda hoe with different controls.
A back hoe on a tractor (3PH) might be more convenient in many instances than my trencher. In many other instances it would not be much different and in a few cases I think the trencher might be better at getting in tight places. Ordinarily I operate it unhitched from the tow vehicle but that is not a requirement and at times may not be preferred.
Have I ever had a problem? Well yes. I lifted it up in the air with its claw and shut the engine off. Then when I lowered it I accidentally set a stabilizer pad on my foot (ouch.) I couldn't reach the pull rope to start it to raise it hydraulically and it was too heavy to pick up. Luckily I had a helper that day or I would have been there until someone happened by. Sounds funny and may have been but it was a serious situation. Nothing broken just a sore bruised foot.
The more I operate the trencher the better I get and the more I learn about how to be more efficient.
It takes a while to rearrange it from towing configuration to digging configuration (and back) but it isn't rocket surgery or brain science. I did weld a couple lengths of square steel tube vertically as carrying accessories for the stabilizer arms when in tow mode, a true convenience.
I find the engine to be easy to start and runs good. Like all small engines it is a bit noisy and to avoid additional long term hearing loss I wear hearing protection.
When you reach out and try to pull the bucket back to you, dragging it too deep, great forces come to play and the digger may move ahead toward the bucket rather than the desired bucket toward the digger motion. This is an operator malfunction not a real equipment short coming. It has a bucket on the end of the digger arm NOT A PLOW. Dig one bucket full at a time and there is not many instances where there is a problem.
What would I change about it if I could? Well, sometimes (friends say usually) I get a tad hyper and wish I could get all the motions it makes speeded up. Also some of the hydraulic controls interact such that doing 2-3 things at the same time is not easy or necessarily the fastest approach. If you do one motion at a time such as curl or uncurl the bucket, raise the arm, extend the arm, swing the arm laterally, or whatever you make good progress and modulating the speed of the movement with the hydraulic controls is easy. If you try to do 2-3 things at the same time it gets complicated as not all the controls interact the same way.
I think it is a good value, i.e. what I paid vs what it does. I have used it for many feet of trenches and I could outrun a covey of shovel armed ditch diggers. I have plenty more digging in store for it later toward spring and am confident I will still like it after that is done.
One short coming is if you have to dig a little here and a little over there and over there is a quarter mile away you need to reconfigure it and tow it as it takes a while to move it very far on its own, pulling itself around like a handicapped crawdad with one claw. However this is not a problem if your site conditions and clearances allow you to leave it in tow configuration while digging. It digs fine while hitched to a tow vehicle if there are no tight constrained spaces where you can't get where you want to be with the tow vehicle attached.
I make no claim that this machine would replace all backhoes in all situations. I do claim that it is a good trencher for the price, has done everything I tried to do with it and I look forward to plenty more digging with it. It will dig dirt that is just too darned hard for me to dig with my FEL on my 40HP Kubota.
Another thing: I use my tractor for feeding the herd, moving large round bales every other day. I haul several 5 gal buckets of feed (3PH with carry all is good for that.) It would be totally unacceptable to have to install and remove a backhoe every 2 days. A machine dedicated to digging works for me. I can't dedicate my single tractor to being a backhoe. For a couple weeks now my pastures are too soft to allow a 4x4 pickup to be used to carry the buckets of feed. I would rut up the field BIG TIME or get stuck. The tractor ruts it a little but the large tires don't sink in as much and gets the job done reliably.
P.S. Our house has been on our backup generator for electricity since last Friday at 2PM due to an ice storm. If we had a 3PH style genset that would be a real nightmare. To use the tractor you'd have to kill all power to the house. To use the tractor effectively you'd have to mount and dismount the genset from the tractor. The point is that sometimes a machine that does one thing and does it well, standing alone and doesn't tie up another useful machine is a far better and only truly practical solution whether it is a generator, a trencher, or pliers or knife or screw driver or... I have and frequently use my Leatherman multi-tool but... it is rarely better at any job that the real thing, just better than not having some capability at all.
Pat (deep in darkest Oklahoma, no lights in sight for days but mine as not everyone has a generator. Now neighbors on a different utility have lights but not us.)
What size tractor do you have HP wise and weight? My little JD650 has 16 HP and is gear driven 8 speed and is about 2000 lbs or so with the FEL. I think the 3 point is rated at 1000 lbs or so... anyway this is the way to go. 
