I bought a Powercal HR-based power meter a few months ago. I think it is crap for someone like me who is in the high 200s. The reviews say it calibrates well with a regular PowerTap meter, but I think that is for someone in the 150-200# range. There's no way I'm only putting out 200w when hauling my fat up a 10% grade.
now I don't have the equipment to do the comparison myself, but if anyone else has tried I would be curious. I have changed my weight on the Garmin head unit, and the power generated is still similar, so I assume it is insensitive to that.
I'm thinking of trying the Stages STageOne crank-based power meter. $700 vs. probably more for a new wheel built with a PowerTap, plus, my current wheel is great (no spoke problems yet) and for me a custom wheel would probably be $1000+. so I am thinking of going that way.