The HovaBator has a heavy-duty heating element that forms a square around the inside of the top. The little disk is the thermostat. You shouldn't use the simple wafer thermostat it comes with--just hook it up to a proportional thermostat instead.

With a proportional thermostat, HovaBators hold their temperatures and perform suprisingly well for such a low cost solution, and they hold 2 clutches comfortably--however, the clutches must share the same space, as egg boxes will not fit inside the unit, and you have to put the medium directly in the bottom.

I have a couple of them, and I have used them for 2 years now. I found you need to add some water mid-way through incubation, but they did the job perfectly, and all viable eggs developed well, and hatched healthy babies.

I'm curious as to WHICH chicken egg incubator you're talking about (particularly since you said it's identical to the HovaBator). The HovaBator is a chicken egg incubator--it's simply usable for reptile eggs as well. Forced-air models aren't suitable for reptile eggs, as they are too drying.
I'm unaware of any incubator that can hold 2 clutches that is only $30, so I'd really be interested in the brand name.
HovaBators are usually between 40 and 60.