Scott,
There have been a lot of threads on this topic. To answer your question, the 4672 is a 3pt BH. There is some reinforcement done on the tractor, but not a true subframe. The advantages of a subframe are:
1. More solid
2. Easier to remove and install
The advantage of a 3pt are:
1. More ground clearance, even when BH is off.
2. MMM can be used.
I have the 4672 and have been very pleased with it. It is designed by Kubota for a Kubota tractor, so I am not worried about all the safety issues that you hear. If I were installing an off brand 3pt, I would worry. Removing and installing is very simple, after some practice. I can install mine in as little as 5 minutes now. The first time took me over an hour of pure grief. It does take practice. I take it off and on all the time now. I will say that it is not as solid as a subframe. It does have a little bounce on the pins. But I have used mine a lot and pushed it very hard without any problems.
Greg