These are super cheap, and so far, very robust and useful. The firmware they come with, tho, needs a cloud connection, and doesn't work with Homebridge. Enter the Tasmota firmware, which makes them into MQTT generating, Wemo-compatible super switches. So far, so good.
Installing the firmware isn't too bad, with a Mac. SonOTA fixes that, and loads up the current latest firmware.
But after that, you're on your own. The firmware has a few options: you can use a URL to load the firmware, or you can download it and use your browser to upload the firmware, and the SonOTA page has a link to the latest version of the firmware.
There is a catch on the internet-site-update tho: you need a decent WIFI signal (75% or better?), or it'll just refuse to load. All my devices are quite a way away from the access point, and well below 75%.
Also, if there isn't enough space for the full firmware - and normally, there isn't - you need to get and install the minimal version first, then install the normal version. I didn't find this part obvious at all, but that's the critical step. (also, this is all on a publicly editing Wiki page, so now, I've edited it)
To be fair, the page does say you have to do this - but they talk about how to do it with a
#define MINIMAL - no mention of what to do if you're using the pre-built ones.