I've got a Kelley 650 3ph hoe on my Ford 1710. Looks like it might be the same hoe, but I've got a 12" bucket. The 1710 is a bigger tractor than the 4100, and it has steel cases. I know the hoe is capable of damaging my tractor, and I take care in how I use it. The soil here is sandy and easy to dig, but I don't try to move big rocks or break large tree roots with the hoe. I also check the mount adjustments about every hour of operation.
The 3ph mount uses two additional top-links that run from near the top link mount on the hoe to a plate that is u-bolted to the drawbar. The links serve to distribute the load between the 3ph arms and the drawbar. The links also lock down the 3ph, which is essential for safe operation. Without the links, the 3ph can lift and pin an operator between the hoe console and the ROPS. Improper adjustment of the 3 links also allows greater load shock to the tractor cases.
If you're going to use the hoe with a 4100, I'd say it would be good to recognize the risks to both operator and tractor and pay close attention to adjustment of the links and also tightness of the mounting plate u-bolts. A smaller bucket might be a good idea. Also, it's a good idea to make note of the sound of the system pressure relief valve. The 3ph is locked down with the hoe mounted. It's possible for the 3ph lever to be accidentally raised. The 3ph will try to raise, which will open the relief valve. Prolonged operation with the relief valve open will over-heat the oil.
Aside from all these dire sounding things, I like my hoe just fine, but do I avoid doing heavy-duty things.