Sem300-ps-vz - Buy on ebay?

I am moving to Surety. I have a DSC PowerSeries 1832 and am planning to buy the SEM300-PS-VZ to adapt it.

I see a whole bunch on ebay at very affordable prices - other than the risk of a defective unit, is there a reason I should not buy from them? I’ll make sure I can return if I can’t register it (i.e. IMEI number is in use by someone else).

The only additional risk is if the SEM is registered to another dealer. You can check the IMEI using the tool below