Personally, I have had good success with it. Once you set it at the right point, which takes lots of fiddling, it is reliable. However if you are buying, the hydrofarm thermostat (just search that on Amazon) is definitely better and for the same price.
They are absolutely not worth your money. They have a terrible reputation, and are poorly made. (open one up and you will know what I mean)
As has been mentioned, the hydrofarm thermostat is the same price and has a much better track record. there are still much better thermostats available, but the hydrofarm will do the job.
I own one and it is so inconsistent that it is 100% useless the day to day accuracy is unacceptable (mine varies 9º AVERAGE daily temp) I cut the probe off as it was so bad I could not in good faith sell it.
Look at it this way your rack houses 4-10 animals? More ? a good thermostat is 100$ so 25$-10$ per animal. One that offers piece of mind and accuracy with high AND LOW shut offs is a bit more but not much say 30-12$ each. A rack is a professional tool buy a professional thermostat for it, this is a small expense compared to heating the room and feeding the snakes.