Great for ensuring that the immersion heater doesn't get left on. The hour setting will heat the whole tank and then, if necessary, you can select 15 minutes later in the day to bring it back up to full heat again. Easy to fit and recommended.
Needs a good sized back box or the right sized cavity particularly with stiff wiring. Very easy to use. Press once for 15 mins, press again for 30 mins press again for 1 hour and press again for off.