Bikes with smart trainers tend to be far more accurate on all readings. I use a Schwinn IC4 spin bike, but it can be questionable on its readings, resulting it potentially more power per /kg giving me more speed. (mine seems to be fairly accurate compared to some others sold in 2019)
Plenty of people use their own bikes with traininers or just an older bike as there set up.
People’s set ups can be found over at