Thanks for the responses and suggestions.
I’ve clocked the Bonts before and really like their form but there seem to be some reliability issues (recognising the possibility of biased, over reported negative reviews).
See Sense is one I was aware of but overlooked – when it’s time for a new rear light I’ll explore that option in more detail as they do look like they fit the bill.
Trace is still in podium position for me – robust, like the idea of mounting it under the Garmin (zero additional bar space needed), reliable and with the option to get it repaired if needed.