The small board fit perfectly for the job I wanted, a power relay and a Sonoff WiFi switch for controlling the water heater via WiFi fit inside

Quite good build quality considering the cost.. it opens a bit difficultly but after a few attempts I managed and I don't see anything noteworthy, everything is fine...

Completely plastic of course but quite sturdy. Satisfactory for its price, but definitely not suitable for main board use, only for local small boards in dry areas.