I have done a quick comparison between my Stages, Assioma, and kickr, and they are all pretty close - well within tolerance from my first quick check. This consisted of running them all at the same time, and recording 3 different files, then comparing power for different intervals. Determining start/end is tricky, but I was able to manually do it well enough for a quick and dirty test.
I do plan to do some more testing and use DC Rainmaker’s tool to compare the files - I think this is the best way to see what is going on, and be able to compare at different power levels and cadences. Since they were all pretty close I haven’t been all that motivated.