[michaelt]

If they've done 500k units, "based on a respun Uno" almost certainly means "there's a atmega328p on the PCB, a 16MHz crystal, and some points granting access to the serial and reset pins"

[DamonHD]

ATMega328p, 32768Hz xtal, in a smart radiator valve. See OpenTRV (for the open part of the s/w and h/w) and Radbot for the commercial product.

[relaxing]

That's a cool product! I wish I could put something like that on my hydronic (hot water) radiators, but they don't have individual valves.