I have measured the surface temperature in fairly use( mainly Wi-Fi connection for 5 devices as Router Mode) with a temperature gun , the highest temperature is around 47 °C (environment is around 27C~29c ).
I think it’s ok for router in this size.
By the way, the lm-sensors package can’t be found in the beta 8 firmware repository source, maybe the router has temperature sensors built-in so the temperature inside can be read out (however the chance is slim since it’s big brother Flint doesn’t have it.) 