I've got the less expensive thermostat from BigApple...it's ok. I think I probably could have gotten the same effect with a rheostat and thermoter probe because I monitor the temps pretty closely myself as it is.

I also have their dual-probe thermometer w/ memory. It's a disappointment. You still have to have the whole unit in the cage because the cords for the probes are pretty short. But other than that, it works well enough. I won't buy another one, though.

I also discovered that Wal Mart has a MUCH better combo thermostat/hydrogometer with the same memory capability. So it measures humidity as well as indoor/outdoor temps. The only difference is that it only has one probe. The "indoor" temp is measured wherever you set the unit, and the "outdoor" temp is wherever you place the probe. But the cord on that one is MUCH longer and easier to work with. I highly recommend this one, even if you do have to have the unit inside the tank.

You can also look into a "temp gun"....it's a device that you "point and shoot" to measure temps on any given surface. Their prices range anywhere from $25 - $100. I've never tried one, but I've never heard of anyone regretting the purchase.

And I think that's all I have to say about measuring devices...but if anything else comes to mind, I'll post it.