At least for me I have run into a few issues with the battery draining quickly or it reporting half charge with brand new ones.
Also have had several instances where it takes forever to calibrate or errors out 2-3 times before correctly reporting calibration.
I also suspect but cannot prove that it over reads. Would need to go properly look at the files but when doing longer endurance rides my np is 10-20w higher than what it feels like compared to my road bike. I will throw it on the turbo trainer one of these days to double check.
Edit: nothing that makes me hate the unit but enough little frustrations compared to the absolute perfection I have had with assiomas to make me want to go get some greener grass.
Edit: One big thing that probably influences the power is the auto temperature compensation that is supposed to happen but does not, although not sure if that is still an issue. A lot of my rides in the winter are on the cooler side and that is where I notice this the most. Bike comes out of a 20ish c room and into a 2-10c environment where I calibrate it then go on my way. I could probably stop in 10-15m and recalibrate but all my other ones handle it just fine.