i dont a have a massive problem with them at all.
I do have a problem wit doctored reading where a clio 172 puts out 160bhp at the wheels.
And i never convert wheel power into fly power no matter how fancy thier calculations are, how ggod the coast down estimates are and how accurate their calibrations and allowances are etc etc.
I take wheel power off it, thats all...
And get friendly with the operator, bring him some biccies or something, talk nice get him you to understand your only really interested in real results as they come, you dont care if calibration is out etc, you just want what the engine is making accirding to the straight reading. And then, use the closest settings you did first time after any mods.
They are the only way though, unless you can afford dyno time.....