These cheapies usually don't come with C-wire power, and I wouldn't have a thermostat without it. My first digital thermostat didn't have C-wire power, meaning it is powered off the batteries only. It ate batteries quite badly and without warning it ran out of power while away on a 5 day trip over christmas, leaving the house nice and frozen.
This is a Honeywell and likely will last a lot longer on a set of batteries as well as give you some decent warning before they need to be replaced, but of course I thought that of the one I had also. C-wire powered is really the way to go, with batteries used only as memory backup.
I'm an outdoor adventurer, science geek, classical guitarist, programmer, photographer, audiophile, and car nut, so I try to help the SD community by posting useful information in those areas.
On the front lines every day fighting the true SD effect: Buying a completely inferior product for a slight discount to the real thing.