If they don't ask you what kind of tires you have on your bike, that's a start to indicate that they aren't going to be very accurate.
I think that until they have force sensor's built into shoes to measure the force you're actually applying to the pedals, it's going to be a pretty inaccurate guess on how much work you're doing.
Powermeters have been around for a while in cycling, and in recent years with price dropping even more so. Doesn't need to be in the shoe, build in to a spider or on crank arm works also.