Well, in case anyone is in a similar position - I fitted the V1 CanSmart onto the ‘21 RT and all works ok. I’m not going to risk trying to update the firmware when it’s working. Just had the bike away for a 3 day trip and no problems - both front D4 2.0 lights, the extra brake led seemed fine with no apparent issues and functions like the strobe with horn still ok.
If it does go belly-up I’ll likely just replace the unit with a new version.