I got the Zass model from Eren Spot a few years back.
Cannot remember the price of them, but imagine most
models should have a min to max heat setting, and like
the Zass, a 1-3 power setting. I find them very good as
they switch on and off when they reach the heat setting
you set them to. Also perfect to set them up with a timer
switch ready to come on in the morning for an hour or so
when the nights are cold.