Be careful, the Garmin GPS-20A - and the Dynon GPS-2020 - are not approved for use in Australian ADS-B installations as they have not been TSO'd, so do not meet the requirements for a position source. In the U.S., they "meet the performance requirements of the FAR's" which is deemed suitable over there. But it's not here.
I've been going through the CARs and various TSOs for a month trying to find a technicality that means I can use Dynons offering, but without success so far.