I'm very satisfied with my P515. I installed it on a Triban RC520. I'm using my 50/34T R7000 chainring on it, but I just received a 46/30T BikinGreen chainring that I'll install next week. I don't have a comparison point on that bike, but I have a powermeter on my Radon e-MTB and values seem consistent, though I forget to calibrate the Magene before every ride... At my very low level, I don't need anything more than that Magene P515. The first initialization is a little bit touchy with the app, connection took forever and I believed for a moment that I had to return it.
I detected one flaw : when the Magene is bluetooth connected to my Coros Pace 2 and my Wahoo Bolt v2, I had short disconnections all the time. But pairing it with the Coros with Ant+ solved the issue totally.