I didn't read the whole thread. I'm sure the general consensus is negative. However, this is my experience:

I installed a Golden Eagle kit on a mountain bike for my father after he had heart surgery for the third time. He also has a replacement knee and severe disc issues in his lower spine. He likes to exercise as much as he can, but that is not very much recently.

Even walking is a big chore after heart surgery. The engine helps him up hills and helps him get started if he's not on a flat area. He gets much more exercise than he was getting before we added the motor. It helped him get his cardio health back up to the point that he could walk a mile, slowly. He also says that people are curious about it and friendly in general when he shows them what it is.

I'm not sure how many of these systems work, but the one I put in for him has an adjustable throttle, so he can barely use it, or use it a lot. It's up to him and I think it's been extremely helpful for his particular health situation. If it matters, before his heart issues resurfaced (congenital ) he was 2/3s of the way done with the Appalachian trail. I doubt he'll ever finish it, but maybe we can ride bikes through the rest of the states!