I am in the market for an AIS unit as well and curious why you are only considering a receiver ? I always thought it best to see and be seen (with option to turn off transmitting).
My apologies for somewhat taking the discussion on a different track, but for a more expensive model (if cost is not the object) the ICON MA-500TR class B transponder comes with a dedicate GPS, VHF Antenna connection provides 3 NMEA in/outputs and a great interface to my ICOM M604 for calling AIS targets.
Your thoughts are much appreciated.
s/v Here and Now