I started out with an Advanced 5600 EFIS in 2013 and a Garmin mode A/C transponder. Then in 2016 added a Garmin GDL-39 for ADDs-B in. In 2018 I replaced the Garmin mode A/C with a Dynon/Advanced mode S transponder in order to meet the 2020 mandate. Big improvement because the mode S transponder is remote mounted and weighs under 1 lb. It interfaces with the 5600 for control.