I'm on the edge to pull the trigger on this, but I need one last piece of info before that.

Based on what I read, there are two crank based system with temperature auto-correction (in my price range). One is pioneer that can be taught to record zero's up to 6 different temperature / elevation combos and auto correct based on this data-set.
What's not clear is whether it's available for garmin users or I have to use their head unit to get this feature? Can someone help me with this?

I learnt from DC Rainmaker's review, that temperature and elevation can be a very real issue for power meter accuracy. He reported 50-70 W difference with Quarq over 20F temperature change. And that's huge.

The other system is Stages. I'm more into Pioneer's PM now because of the dual side recording, but I'd rather have a one sided power meter than 10-20% difference in watts due to temperature / altitude changes (or several calibration on longer rides).