These are ok if you are on a tight budget. I have one on one of my racks, and so far so good. The temp. does fluctuate a few degrees, but I will be replacing it at some point with a better one. On my incubator and the rack that houses my females, I have a Herpstat II.
Lots of people on here like them, thats why I picked one up and gave it a try. Worth the money!