Power Meters / Powermeters (SRM, Powertap, Quarq, Ergomo, Vector, Stages, power2max, P2M, 4iii, InPower, Cinch)

Stages are a kind of halfway house between the PowerCal and a proper powermeter, but given their price I can't see why you'd get one over a Powertap.

Can you explain this? Surely Stages is the same as Power2Max, i.e. using strain gauges on one crank and then estimating the power for the other leg (not that knowing the left/right balance seems to matter in the end)? Or have I missed something?