There are a lot of "used" GS's available (mostly people who bought with P2V+). I am planning on getting one but I am curious about the model discrepancies. DJI is notorious for making small adjustments without explaining the details. For example, I have noticed some air-end data links have a metal casing and some a factory shrink wrap. I assume the shrink wrap is newest and preferred. Are there other differences I should pay attention to when buying used? Is there a way to tell which 'model' the GS is using the S/N or date code? Anything else I should watch for with a used unit? Thanks!