We bought one (just the M1 AIS, not the VHF handset) last winter because we were so happy with the XB-8000 on our previous boat. I installed it in Florida for our trip up back up the east coast, not only for the AIS, but also for the anchoring app and also for a position fix via wifi on an iPad charting app. Like I mentioned in another post, I bought it days before it was announced that Garmin had acquired Vesper. Had I known, ,I might've looked more closely at another brand, but maybe not. I do like the Vesper anchoring app.
We did have an issue the entire way back, and that was not being able to turn off the internal heading sensor. Due to the M1 having to be mounted near other electronics, the sensor always had a severe deviation to the heading, causing our charts to be skewed, in the heading up mode, sometimes as much as 30-40˚. I spent quite a bit of time on the phone with a Garmin tech, who was obviously not at all familiar with the Vesper unit. I was assured I would get a call back after they contacted the Vesper gurus in New Zealand. I never did get a return call. Fast forward 6 weeks later for the 2nd leg of our trip home from SC , where we noticed another boat on our chartplotter whose boat icon was "crabbing". I hailed him on the radio and he told me they were having trouble with their new AIS. I asked if it was a Cortex and his surprised reply was yes. Finally , fed up with our own boat "crabbing" up the east coast, I called Garmin again. This time, they were fully aware of their problem & had an answer for me.
1) I could wait for a new software update
2) They would send me a garmin smartcast sensor to add to the nmea 2000 buss (if the Cortex sees a "HDG" message in the nmea 2000 data stream, it uses that and ignores the internal sensor).
A week later I installed the sensor and for the most part, it fixed the skewed heading issue, although the chartplotter still briefly switches to the internal heading of the Cortex sensor, but not long enough to be a nuisance.
All said and done, I guess the Cortex was the best AIS for us.