Cadet in-wall box heaters with analog control

My friend has home depot cheapo in wall heaters. The 'thermostat' is roto-dial reostat with a huge variance. She has 6 of these throughout her small home.
She's going to move to HE, and I'm suggesting some basic smart thermostat for each cadet, and a 'central' thermostat - "One ring to rule them all - ... bind them" sort of approach.

Has anyone come up with a sensible solution and have arguments for or against my approach?
I have found this for a line voltage thermostat (seems pricey tho):

If she likes everything the same temperature, that could work. There can however be benefits in having some room setup cooler to save on electricity.

I have changed all my thermostat to Sinopรฉ Zigbee a while back and love them! They can show the outside temperature along with the inside temp and the time. Extremely useful! They can also be setup so that the display is only on when required (certain times, motion, etc.).