AS GR4 or AS GR16 with Matrix 12

Good morning, I did a search and didn't see this topic covered.

I recently purchased a second hand boat that came with a Humminbird Matrix 12. After doing some research I decided that I would be better off purchasing the GPS accessory for the unit rather than buy a handheld GPS unit.

In the manual it says that the adaptor is the AS GR4 unit. When looking on the Humminbird website the accessory tabs lists the AS GR16. Is there a major difference between the units and can I use the GR16 on an older model Matrix 12 (I don't know the exact age of the unit).

I can get the serial number if that gives any indication on the age / suitability of the unit.

I have checked eBay and can only see the GR16 for sale, and being based in Australia the units bought from the store are considerably more expensive.

Thanks for your help.

Regards,
Lachlan Moore