I wasn’t ready to shell out for a new headunit and I was interested in smartwatches, so I found a model from this list that has phone and/or wifi connectivity and was available second-hand (also no asterisk next to the name): https://support.trainerroad.com/hc/en-us/articles/360032333891
I got a second-hand Fenix 3 HR smartwatch for 135 AUD (75 GBP). I use it for recording and timing workouts, but I still use my Pioneer headunit for displaying realtime power, lap times because following very short intervals is tricky with a watch only.