Yeah the digital will be a better investment. You might have to play around with the set up a little bit to get it where you need it to be. A digital hygrometer would be better. Check home depot or lowes and you might be able to find something cheaper then at the pet store.
Put one probe in the hide where the UTH is, under the substrate and touching the glass. This is the hottest point your snake can get to. Put the other thermometer probe on the surface of the substrate on the opposite end of the tank. This is your cool side or ambient temp. Plug the UTH into the dimmer switch and the dimmer switch into the wall. Mess around with the dimmer until your hot side temp reads around 90 degrees.
I would start with one lamp in the middle of the screen and see what your cool side thermometer reads and mess around with it from there. The less lamps you have to use the better. The lamps will suck all the humidity out of the air so you need to mist more. So if you can avoid the massive decrease in humidity, everyone is better off.