I have run a Power2Max crank-based power meter on my V20 for the past five years. The V20 is my only bike so this works for me - I don't have the need for a pedal based system. What I like about this product is that it just works. I only have to change the battery every 12 to 15 months and it works beautifully with my Garmin Edge device.
Power2Max has previously sponsored UAE Team Emirates and Movistar, and currently sponsors EF Education First - which means they get a lot of input from World Tour level pros.
Regarding comparing power from each leg, the Power2Max provides that data as well. I don't know how it is measured and calculated - though frankly I don't particularly care. I have the data available to me after every ride.
All that said, if I were buying a new V20 right now, I'd also take a serious look at the Sram Quarq options. The website bikeradar.com have the Quarq DFour DUB on their list of the best power meters in 2022.
I also suggest checking out the power meter reviews at dcrainmaker.com
Hope this helps...