I like them, have them mounted on my buckets.
As was stated, if you use a water bath for temperature control, you'll want to make sure you mount the thing horizontally above the water line.
I've also got a few from the fish section of the petstore (from when I really wanted to check the temp and didn't have access to my not-so-local HBS for a day or two). Cheap and bright, but mine only go down to 64F.