For the record I’m on my 5th 4iiii Precision 5800. The first one just started giving me bad readings out of the blue mid-ride. The second just didn’t turn on straight out of the box. My third gave me a calibration error after washing my bike. The 4th gave me a calibration error after sitting in direct summer sun for a lengthy time. My fifth is going strong, came from a different supplier in the UK.
Have to say support from 4iiii has been excellent and with that said I thought my luck had to be in sooner or later so I stuck with the company.
My takeaways for 4iiii are don’t hose the crank arm directly and also keep the o ring lubed up and don’t subject it to extreme temperatures.
I have 2 bikes set up for 4iiii, both with 5800. I swap these around in November and April.