Lots of folks make the argument that pedal based are easier to swap from bike to bike, but given the relatively low cost of power meters, I simply have a crank arm PM on each of my bikes. A small investment on a bike I'll ride for 5-10 (maybe more) years saves a lot of swapping pedals from bike to bike. I really don't want to swap pedals when I swap bikes. I want to hop on and go.

I've used a single sided 4iiii on my primary race bike for the past 3 seasons without a problem. My other bikes have a Pioneer double sided crank arm PM, and a Stages crank arm PM. I've checked each of the PMs for accuracy and consistency against an old Power Tap wheel and my Kickr Core trainer. All are accurate, consistent, and reliable enough to rely on for training and racing.

I'd read up on the Shimano PM's reputation. When I built up my last bike, I considered going with Shimano, but was steered towards the 4iii by reviews, friends, and my LBS. Maybe they've fixed those problems. I don't know.

Finally, I have a double sided power meter on my 2016 Propel. At the time, I thought injuries and sciatica would make the two sided data useful. In practice, it wasn't, so I saved myself a lot of money by opting for single side crank arm PMs for my next two bikes. YMMV