I don't put much into trying to power balance your legs. To train one leg to get stronger is to not train the other leg to get as strong as it could so your over all power is lower. Your weaker leg will catch up to a reasonable balance fast enough. Talk to your PT person about it.
Bikes are real efficient in converting leg power into motion. And if you look hard you can see that bikes move in surges as each pedal stroke occurs. So I can't fathom why you'd need to have it surge equally with both legs. Though I can see where people get the false idea that a smoothing of the power is better. Admittedly I have not been interested to read in depth on the subject. So if any has a good rational I'm open enough to consider it.
However if that is your excuse to get a dual sided PM, then go for it. I'm trying to justify to myself getting the right side PM to go along with my left side PM.
I'm happy with the crank arm base PM's. They seem to be the less expensive right now. I think hub based PM are long gone. My PM is 4iiii. But others are out there too for way less than pedal based PM's.
Any thoughts on how much benefit I will get from a balanced effort and power monitoring?
You'll know if you been fibbing to yourself how much power you put out! <grin>