Hello everyone...my apologies if this is covered..I have searched and found the table of which M Series, but how can I be sure which one I am buying has the correct chipset/firmware?  I'm on Ebay ready to purchase a bullet M* but want to be sure I'm getting the correct version. 

Is it safe to say that all bullet M2s are safe?  Basically looking for either a serial number matrix, firmware ID, or something to allow an online purchase of the correct hardware. 

Thanks for a great resource. 

73,

Paul