Is this Under tank heater appropriate?

[ladybug15057]

A UTH on the side of the tank is about worthless. It does nothing to warm the substrate, and chances are your hermies may need to pile on top one another to get the warmth from it. On the side one is lucky if it warms the sand 1 inch in from where it is mounted... maybe 2 inches?
The UTH should go on the outside bottom of the tank on one side or another.
The stress crack, yes it can happen if the glass is hot from the UTH and cold water pours down to the warm glass. So do not be pouring cold water over where the UTH is.
The UTH alone will take 2-4 days to warm the sand so you may wish to preheat a little that will be going on the warm side of the tank... only to a tepid temp.
Make sure to pitch the little rubber feet that came with it. Use either 1 inch by 1 inch wooden blocks (or legos) under the corner frame of the tank to hold it up off of the UTH. Or if mounting on a larger tank (on our 40 gal breeders and 55 gal) I use 1 inch by 2 inch strips of wood to hold the tanks up... IMO more support.