I've been using the stages meter for a little over a month with great success. I ran a powertap simultaneously for a while because I was skeptical of the low price.

It does not need to be calibrated. The temperature is sampled every 20 seconds and small corrections to calculations are made. You should be performing a zero reset prior to each ride. The crank arm should be at the 6 o'clock position with no load during the reset.

My meter came from the factory with the original firmware, which was buggy and its accuracy questionable at best. I'd definitely verify that you're running the latest version before training with it.