High amps usually
indicate a strong motor, however with no load it's not always an accurate assessment of a motor. A good motor could pull low amps, but be fast on the track. Likewise, a motor could pull 10+A but be a dog. The best way you can use the motor monitor would be to compare motors on it to the numbers you get from a motor that you know performs well on the track. Also, make sure nothing is binding, because that will make the motor draw more amps. (squeeze the armature when its running and the amps will shoot up)
Hope this helps somewhat, someone else will have to help you with the silver can, I don't jack about those.