I’m thinking about picking up some Sonoff MINI R4-units for my old light switches, however my house is plastered with double switches.
Does anyone have practical experience whether this is an allowable wiring configuration?
You can’t connect like that. MiniR4 has only one output (L out). Connector S2 is used to connect a single switch.
In the diagram you have one bulb. For what purpose do you want to use double switches?
For controlling other devices not physically connected to that Mini.
then maybe you can use SONOFF S-MATE Extreme Switch Mate