I have a couple of the TH16 models with the two different temperature modules connected so far. I have waited to load new firmware on them because of the limited storage space these have. I have a batch of the add resisters on order to make additional connections through the jack that will give me the ability to control more devices with each unit. Also am considering ordering a few of the storage upgrades so I can add over the air updates to the firmware. I don't want to have to remove the unit each time I decide to upgrade functionality.
Here is a good link to read about upgrading the flash storage.
Here are a couple good videos that talk about customizing the Sonoff devices.
I have been waiting on Wigwag to get their act together so I can decide how I want to configure the Sonoff devices. I also want to figure out a good way of still being able to control the lights with a standard light switch and the sonoff device. The second video talks about doing that a bit too.