@Thomas_Alsop: It is sad that people treat Zpower in that way. But there is a good reason why the zpower got a bad name. There are a lot of zpower rides that have a bad setup and think it is normal to do a zone 2 ride at 300w.
But there are trainers that are pretty good and consistent. I have two zpower trainers that I tested against my power tap wheel and they are in the ball park ±5% most of the time.
I would not mind racing against someone that read 5% high, as long as he always read 5% high and he enter the correct Cat.
If you do a FTP test with your trainer (Zpower or Smart or power meter) and you have a accurate FTP number and you put in your correct height and weight then I will race you without question.
the only place where I don’t think we should see Zpower is in the A and A+ group, once you reach that level you need to have something that is calibrated and trusted. the reason i say this is because if your trainer read high you may ride in the C cat vs the D but it it read high in A then there is no place to move up so the playing field can’t be level anymore.