Hi there
I have an old Bkool Pro wheel on trainer. Have anybody made an comparison between a direct drive and a wheel on hometrainer on how precise the watt measurements are ? It seems to me that it is harder to do high watts on the wheel on trainer, than when I use a spinning bike with watt measurements.
You would probably get better accuracy with a direct drive trainer because it has less variables to deal with , like tire pressure and drum tension.
It really depends
I have used:
Tacx Neo (Direct Drive)
Tacx Flux (Direct Drive)
Tacx Flux 2 (Direct Drive)
Tacx Flow (Wheel On)
Elite Drivo (Direct Drive)
elite Zumo (Direct Drive)
Bkool Pro 2 (Wheel On)
I have also used two pairs of assioma duos. The two sets of pedals and the tacx neo and elite drivo were all within +/- 1 or 2 watts so i’m fairly confident they were all very accurate (would be very odd if they were all exactly the same level of wrong!)
Tacx Flux 2 was slightly better than the flux 1 but both were within about 10 watts at 250 watts so pretty good.
The flow is okay(ish) once warmed up - within about 5% or so after 15 minutes of riding if properly set up/calibrated
The zumo is a disaster miles off no matter what I do to it! (but i have pedals so not too much of an issue for me!)
the bkool pro was quite far off too waqs never really convinced by it saying it didn’t need calibrating and just using the bike weight to hold it on the roller meant it bounced up and down a bit which can’t have helped the power accuracy.
so to sum up - Direct drives will probably be better, the more you pay the better they will be (to a point) but they aren’t guaranteed to be good and some wheel on trainers are pretty good (the elite Tuo is meant to be pretty decent but not tried it myself)
TL;DR? direct drive will likely be better but not always
Thanks for the valuable input. My Bkool alså bounces a bit when driving, which I guess doesn’t help. I don’t know if it can be calibrated, I will have to look into this. It is the old Bkool Pro, so probably not. I had to force an old firmware on it, to make it work with Zwift.
I will probably go with the Tacx Flux 2 in the long run, but for now I will live with my Bkool Pro.
I have recently used this (my sister has one and I used it whil eI was staying with her) I tested it against my pedals because, well why not?, at it was good, has a pretty smooth riding experience too so if you do go for that I don’t think you’ll be disappointed. Will be noticeably better than you bkool.
Having tried a few of each I tend to prefer tacx to Elite trainers but that is just a personal preference
Do you think it’s too low, too high, or just too variable. I have a Zumo but nothing to compare it against.
mine is about 15% low, it is pretty consistent but consistently terrible!
Ah well, that just means I’m fitter than I think I am 
yours might be fine but mine is awful
FWIW I was able to borrow a pair of Garmin Rally pedals for a short time today and did a Zwift ride with those paired to my Edge 530 and my Zumo paired to Zwift as normal. As expected the Avg power was about 4.5% more with the pedals. Easily accounted for in drivetrain losses. However, my Max power was measured as 641 W on the pedals and only 553 W on the Zumo.
If I could keep the pedals longer I’d do more testing - at various steady power outputs and with more powerful sprints.
i have my old steel bike in a wheel on trainer, use garmin V3s power pedals, ( akso use same pedals on my road bike)
don’t need to worry about tension or tyre pressure 
( also feeds power BT to zwift atv via companion app and ant to head unit )