Testing against a Kickr isn’t that useful, it’s not what most would consider a reliable power source. I think all these power threads are relative though, if you have a baseline, and can improve your power output then absolute accuracy isn’t that important. A lot of us strive to get as close to accurate as possible because we have multiple bikes with PM’s, so we want confidence that 300W is the same whether on the trainer, bike 1, bike 2, etc.
Unfortunately, it’s hard to nail down a high level of accuracy, and even if we could there could be a number of factors that would skew the numbers over time.
@wodeson, what software is that?