Not to be redundant or not trying to call anyone out, but these are the types of threads that confuse the newcomers to the hobby.
Never guess your temps. That I agree with. Yes, you should invest in either a digital thermoMETER with probe (or a temp gun) to measure the temps inside the hot hide...
That is correct. The thermoSTAT has a probe that goes on the heat source. This probe will "measure" the temperatures to tell the thermostat when to turn on or off based on where you have the dial set.
Again, this is not a one-or-the-other deal. A thermoMETER with a probe is NOT a replacement for a thermostat. I recommend using the thermostat you have now, but getting the thermometer you need to use in conjunction with the thermostat to make sure you know the temps you're getting so you can set the thermoSTAT accordingly.
Again, this is bad advice telling a newcomer to return the thermostat they already own to get a digital thermostat OR a temp gun. You need BOTH. You need a way to REGULATE and to MEASURE.
Sorry again for the redundant post, but I feel these things need to be clarified before the OP goes out and returns the thermostat in favor of a thermometer, then starts another thread when the temps are too high where he will be blasted for not having a thermostat...