here is my setup using an old Sonoff TH10:
I've not found a way to log the temperature yet, but once I've got that sorted I'll spend a couple of weeks logging the temp before changing my heating strategy.
My thinking is that I'll cut out the morning heating cycle which runs for an hour currently, and change this so that the sonoff switches on the boiler and heats the tank but only if the measured temp drops below, say 40C, in which case it'll heat the water until it gets to 45C and then stop.
It would be great if there was a way to log all the boiler burns on a chart too, but I doubt there is an easy way to do this. The switched live on the Sonoff goes straight to the DHW terminal in the wiring box, so it can switch on the water independently from the Wiser controls, giving me both scheduled and temperature based controls. In fact, I don't need the wiser DHW controls at all any more, in theory.
Drilling the hole for the sensor was scarier than I thought, as the boiler sleeve is sheet steel, and once you pimch through, the insulation provides no resistance whatsoever! So be careful. Still not sure if I have the best contact between the sensor and the tank surface, so am experimenting with tin foil to see if I can increase the quality of the contact.