I bought a used GXM sat antenna for my Garmin Zum 550 on eBay. Square Trade is sending me extended warranty coverage options for this item. Only cost less than $20 for two years. Anybody use the GXM antenna and has anyone bought the Square Trade warranties. I see a lot of refurished units on eBay so I wonder if there is a problem with them and making it worth while to have the extended warranty, cause there isn't any warranty on used.