It's a way of buying a non drive side crank arm, if that's what you mean.
So does Evans have your drive side crank arm, and have been trying to find you a non drive side arm? Buying a stages arm would be an expensive but immediate remedy to that problem.
What about buying 165mm Stages Hollowgram and then fitting a P2M - is that possible?
https://www.powermeter24.com/uk/stages-power/stages-power-meter-road/stages-power-meter-cannondale-si-hg-g2?gclid=CN3G17Hx_ssCFTAz0wods5MFoA