I don’t know anything about the Raymarine AIS but can recommend the NASA ‘engine’. It costs around £110 and works fine. It needs a VHF aerial and 12V inputs and provides the standard AIS NMEA output at 38.4KB. I use it into a laptop computer but I expect it will drive into the C120 using NMEA without problem (once you have sorted out which wires/connectors to use!).
I rate AIS highly. On both channel crossings this summer when the ‘collision’ alarm sounded I was able to identify the hazard by name and call them up on VHF. In one case, the freighter executed a 40 degree turn to pass astern of me – he clearly hadn’t seen me (or was playing ‘chicken’ but was exposed to the world on channel 16)!
Get one – it’s well worth the investment in open water. However, you will need to turn off the collision alarm in the Solent otherwise it will sound constantly!