My stoker and I both have Assioma power pedals.
I have on occasion had curiosity to wonder: "how much effort is that stoker really putting down", and these do let me check, but only with a second head-unit on my handlebars (because you can only pair a head unit to one powermeter).
My stoker is remarkably good-natured, but if yours is not, I caution against such foolish and expensive pursuits.