I am not going to comment on the Chinese toys since I can lose my insurance by getting involved in them. My comments below are about the Coltri or Bauer stock small compressors (not the Daystate which is Coltri made).
Duty cycle has to do with the compressor itself ... not the motor which has it's own duty rating. In order to take a continuous duty machine (can run 24 hours a day at max pressure) to intermittent duty, the manufacturers had to reduce crank and bearing size. This reduces size, weight and cost. Temperature plays a small part in the rating, but stress on the system is the key component. The small $2700 compressors can pump all day long one tank at a time to max pressure (4500 psi). As long as you are only filling one tank at a time, the maximum stress occurs only for a short time as the compressor gets up to 4500. However, if you hook up a bulk tank, you greatly extend the time that the compressor will be at the higher pressures and will slowly but surely be eating away at the crank shaft bearings and races as well as the piston pins.
So, fill one tank at a time and you are golden. Fill a daisy chain of tanks or a bulk tanks or two and you will be calling me for repair parts sooner or later.
Ray Contreras - Owner CompressorStuff.com