yes I think you are right it was just a passing thought when I saw the adapter and I have 3 pt. stuff I was thinking would be nice to be able to run. the motors had all kinds of hp ratings some pretty unrealistic what they were claiming. I kinda shelved that idea for now anyway.
You have to match the hydraulic PTO motor on the adapter to the hydraulic flow on the loader.
For a given hydraulic flow and pressure from the loader:
Larger displacement motors will turn slower but will produce more torque.
Smaller displacement motors will turn faster but will produce less torque.
I got a call from a guy who bought a PTO adapter from Skidsteer Solutions. He told them what loader he had and they selected a model and shipped it out. He tried it out with his PTO tiller. As soon as the tines contacted the ground they stopped rotating. After a number of phone calls with Skidsteer Solutions trying to resolve the issue, I got a call.
The issue was not a problem with the loader or the attachment. The issue was the PTO motor was sized incorrectly for his loader. I calculated the optimum displacement and he got back on the phone with the vendor.
Once he got an adapter with the correct size motor, the tiller worked well and he was happy.
An over-ride clutch would help, but a better solution is to add a "Tee" fitting to each of the lines that are attached to the loader. Connect the "Tee's" together with a check valve. This way when you turn off the flow from the loader the PTO motor can continue to rotate since the oil leaving the motor will travel to the TEE, through the check valve, through the 2d Tee and back to the motor. This allows the motor to coast down. The down side is you can not run the motor in the reverse direction because the oil from the loader will just open the check valve and return to the loader.
Also be aware that brush cutters do not like thick fine stem grass. It is one thing to have the blade shear off dry sticks. It takes a lot more power to cut thick fine stem grass where the load on the blade is heavy and constant.