I’ve been installing the Sonoff devices all over the house and wiring them up to OpenHAB via MQTT over the last month. The open firmware mentioned - https://github.com/arendst/Sonoff-Tasmota/wiki - is lovely, and pretty easy to install. Some of the soldering can be awkward (the basic Sonoff relays are fine, but the Sonoff Touch is a nightmare :P) but it supports over-the-air updates once you’ve got it up and running for the first time.
I’m waiting on a couple of things and then there’ll be a few new entries in my automation blog series on it - I already covered installing Mosquitto in the HestiaPi Classic posts, so I’ll build on that - and there’s going to be a post on using the Sonoff TH10 (with temperature sensor) as a remote thermostat for Hestia 