I also bought the National Geographic one, just the other day. It seems to be reading right on with my exo terra. I think the accuracy of some of these depends on what you're using them for. I'm using them with grey tree frogs, who I do not need to mist regularly because the water dish has a bubble stone in it which seems to maintain the humidity really well. I think if it was a species that needed a higher humidity and required daily misting, I might run into trouble with them. As far as I've seen though, the digital therm/hygrometers that do really well run pretty expensive.