The may be more expensive from Amazon, however, I am suspicious of buying on eBay, especially for things like this SD Card where it needs to have never been installed on another vehicle. I guess the bottom line is that you can buy it from another seller, however, make sure you are buying from a reputable source and you can return it if it does not work.

 

I purchased from eBay with no issues. Make sure it’s a highly rated seller. My purchase was from a seller that had a 100% rating.

 

I also observed that my 18' Mazda 3 Touring doesn't have an external antenna anywhere, but the car has the navigation button on the center control for the navigation. Will I need to get an external "shark fin" antenna installed for the navigation once I get the SD card?

 

when you select navigation, does it show the compass and does it appear accurate? If so, I would assume you have what you need to activate the navigation system.

 

Yes, the compass and bearing display are accurate when driving. It was just weird to see a car with a hidden or internal antenna for the radio and navigation.

 

GPS antenna is hidden in the dashboard.