Quarq is a more affordable (but still considerably more than Stages or PowerTap), crank spider-based alternative to SRM. Like SRM, it leaves wheel and pedal choice down to you.
You’re most likely to buy a Quarq system – available in a number of models across varying price points – as a custom built crankset, which limits selection (Quarq is owned by SRAM).
Quarq measures power via five strain gauges and features include Power Balance (available on all models except the Rikon), which estimates left/right power balance.
Pros: Crank-based system can be used with any wheel/pedal selection, Power Balance, cheaper than SRM
Cons: Limited to one bike, crank selection