That will be fine. You can even get one of those other thermometers you posted from home depot was it? With the suction cup to stick on the glass just above the substrate on the cool side. I think those are alot cheaper than the ones sold especially for reptiles. It seems just by putting the word "reptile" on it make it cost more when it does the exact same thing.

I personally have a few of those small accurite therms that have no probe and only tell one temp. I use them in my tubs in my racks. Then I only use a couple of the combo ones with probe in a tub near the floor and one in a tub near the top. Since they are all heated by the same long strip of flexwatt I only need to double check temp in a couple places. The other single temp ones are just to monitor the ambient/cool temp near the front of the tubs. I don't use any thermometers that are marketed for animals. They are simply too expensive.