The main differences between the TireMinder TM66 and the A1A are the A1A has a 40% larger screen (slightly more than an inch larger), a dedicated ON/OFF button and mode indicators. Also, the TM66 is exclusive to Camping World.
Besides those differences the TM66 and A1A have nearly identical software.
As for our TMG400C, it has been retired since the beginning of 2015.
For a detailed comparison chart, please click here: TireMinder A1A, TM66 and TMG400C Comparison Chart
For a detailed comparison chart for the TM-77, A1A and Smart TPMS, please click here: TireMinder TM-77, A1A and Smart TPMS Comparison Chart