I wonder if their is any kinda thin glass that is not insulated but strong enough to not break?It depends on what kind of fish you are going to have in this divided tank. If it is going to be a Betta in each side then yes, you will need 2 heaters. If you are going to have a Betta in one side and cooler water fish in the other side then no, I don't think you will need the second heater. Some heat from the heated side will radiate out to the unheated side through the glass.
It should be az its designed for that. Ive never used one. Just saw it once at the lfs.
I think I saw them at the store by the betta tanks. May be too small of wattage though. Probably more for like bowls.I thought those were for reptile tanks only ? Did they start making them for aquariums? I know the reptile ones crack the glass. 2 times I've had glass crack from heating pads in my reptile tanks. One really cheesed me off because it was 120 gallon fish tank, not a reptile one so I could have used it as a fish tank after, but instead I had to throw it out.