Hi Alex,
complicated question, fun :-).
The road power meter is specified from 30 rpm upward. When you start it will take a little moment to get an accelerometer signal. Since the track is super smooth the signal will be of great quality, so data will be good.
I don't quite follow your one leg conclusion - why would the force be from one leg only? Torque is total torque - ie how hard you push on one pedal and pull on the other. Especially at low rpm I would expect the pull component to be significant.
Regarding the acceleration: since the acceleration is very gradual and your are on a smooth track the conditions are ideal. There should not be a problem with it. As to how power changes during a start phase, that's not my area of expertise - more one for sports physiologists :-).
Re power: sampling is done at 50HZ and torque (which varies A LOT) over a pedal turn is smoothed, ie averaged, so you can actually read the data. The data is updated every second, as per the ANT+ protocol. If you took the peak torque you would overestimate power.
Re the force platform comparison: again, I'm not a sports physiologist, to mind came that pedaling involves both legs and the duration of the force makes a big difference.
I hope this helps and that I understood your question right.
Best
Nicolas
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power2max
http://www.power2max.com/northamerica official power meter of Movistar Team