I use 2 of these and they're great - I've never had a problem.
Nice large display, and the thermostat probe is also a thermometer.
I think I paid around $60 each for mine.
The alarm can be quite annoying though, especially if you have your thermostat on a timer like me so there's no heat over night. It means every morning when it turns back on, the alarm will go straight off because it's so cold.
At the very least though, the memory seems to last for quite a while so if you lose power or use a timer, it will store the set temperature / timer settings for long enough.. So if you don't want to fork out the money for a day/night thermostat and are happy with no heat at night, it will work fine on a timer..
The only way I've found to 'disable' the alarm is to take the back cover off so the speaker is visible and snip one of the wires to the speaker? If you press a button while the alarm is going off, this seems to stop it, but only temporarily I've found.