Ok, so to follow-up on doing a comparison between my Wahoo Kickr, Favero Assioma Duo and Garmin Rally XC200 I did a static weight test on the Assioma Duo (which came in as on spec). Then calibrated the Kickr using the standard spin-down and calibrated the Rally XC200 using the in-app zero offset.
I rode an identical workout in Zwift using identical equipment except for switching the pedals. The first data set compares the Kickr with the Assioma Duo.
The data align closely, with the Assioma Duos reading ~1.5-2% lower than the Kickr. Given that the static weight test was within spec for the Assioma Duos, it seems likely that the Kickr is reading a little high as the Kickr should read ~3-4% lower than the Duos owing to drivetrain losses. In any case, they are close enough to one another to be useful from the standpoint of being able to use either the Kickr or the Assioma Duos and compare between workouts, although I tend to just use the Assioma Duos as the power source when I’m Zwifting.
Comparing the Kickr with the Rally XC200s looked as follows:
The XC200 read ~9-10% higher than the Kickr (~11-12% higher than the Assioma Duos). Unfortunately, I can’t perform a static weight test with the XC200 as I don’t have a Garmin Edge head unit (I’m using a Karoo 2 - see my interaction with Garmin Support above).
Seems to me that the XC200 are way out of spec. Be interested to hear thoughts on this.