I have a Garmin chartplotter and so did think about getting a Garmin AIS transponder - the benefit seemed to be better / enriched integration on the display and the ability to call up an AIS target vessel by DSC from the MMSI data, without having to manually enter the number.
BUT - I didn't think it worth several hundred pounds for that functionality... Especially as even my bargain transponder was £399 (inc VAT). But all depends on your budget I guess.
I still get all the data I think I'd need on the chartplotter via the generic NMEA connection (including proximity alarms etc), which was fairly straightforward to set up.
Hope this helps