I compared the ones I have to the calibrated ones I have in my cigar humidor and they were right on. I really couldn't believe it. I figured they would be a good ways off but they all agreed.
As far as sticking them I just clean the cage wall really well with alcohol and use some good Velcro. That way if the snake does pull it off they will simply separate the velcro and not expose the sticky side of the strips. My GTP will climbs on his and it has not fallen off. My ETB did knock hers down and kept doing it so I now just have it sitting on a large flat piece of petrified wood. I have another that I was using in my Hoggy tank but I got a hanging hide for him and had to remove it because of space.