If you're going to sell it anyway, just go double sided. Vectors or whatever if you don't want to change your cranks. Unless you pedal at the same L/R variance for every single second of your ride, the data from a left-only is going to be inherently wrong. What's the point in that?
That makes no sense. Buy a second hand Power2Max from @eyebrows, he seems to have an endless supply, then keep it because it's good to track numbers over time.
To quote yourself
" I don't really care that much about fitness/numbers etc."