We tested it, and with our usual usage pattern of using the summerhouse every 2 weeks, the brand new fridge uses less power while powered for the 12 days between departure and arrival, than it does cooling down when powered on at arrival.
Despite being brand new, it uses 6-8 hours to get from 18C to 5C. I guess because it's brand new it is well insulated, so less cooling power is needed once it's cooled down, which translates to a weaker compressor with less power consumption.
As for the Raspberry Pi, it runs idle for 99% of the time, consuming _at most_ 1.15W. That amounts to 0.8 kWh in a month, which is about as much as a TV uses in 2.5 hours, or about a quarter the power consumption of a Sonos One Speaker sitting idle [1].
The total power consumption of the summerhouse uninhabited is ~1.8kWh/day, which includes the heat pump, fridge, internet modem and router, Raspberry Pi, Security Camera and a couple of hubs for IoT.