I've been using a cycleops H2 for the last 12 weeks fine, and picked up a pair of vector 3 and an edge 530.
Without going into the frustrating detail that is the android app, updating firmware, having to replace the battery internals etc. The power is considerably lower than my H2.
Anywhere from a 10%-15% difference, which translates to a consistent 20w-30w difference.
You can see this for yourself in the below links:
* https://analyze.dcrainmaker.com/#/public/39d44ce5-e5d6-48e1-6988-48732205fccb (ERG mode zwift workout)
* https://analyze.dcrainmaker.com/#/public/50d40e1a-b227-4553-699e-6ea628160696 (ERG mode zwift workout)
What I've tried:
* Calibrate before every ride, spindown calibration of h2 before every ride
* Had pedals stock, performed angle reset
* 'Serviced' pedals (new battery cover and connector bit, regreased and torqued the middle part), angle reset etc.
* Performed ~4 full-gas sprints after installation
The freeride I did after the service seemed better, ~8w difference @ ~4% difference which is within spec IMO, but my next ride onwards is back to rubbish 20w-30w difference (10% or worse). Both ERG and freeride are off, and it is consistently off by the 20w-30w.
In the above links, you can see my L/R power is off somewhat, with my left being always substantially lower than the right. I think this is a big factor here.
One thing I noticed is the left pedal from the factory was extremely tight, it would barely rotate whereas the right pedal spun freely. I fixed this by servicing as above, however left is still down a lot which I don't think is due to my physiology. If you add the missing watts from the left pedal, it works out to match the trainer.
Unfortunately I cannot afford another power meter to validate, nor have any friends locally that have a power meter. The bike shop told me to speak to Garmin to sort out.
edit: if anyone is in Melbourne, Australia, and wants to go for a ride and a test I'll happily buy several beers
I've submitted a case to Garmin support, however haven't heard anything back just yet. Cheers.