I've never seen one with a dynamic setting and two thermometers, but it makes a lot of sense that they should make one. No need to run the fan when the outside is not more than 10 degrees (F) cooler.
One option that would avoid putting a DIY gizmo on your home electrical system in an abusive environment* is to run some romex down from the attic to a convenient location and install a timer switch. Then you can configure it to be always on in the spring/fall, always off in the dead of winter, and run it on a timer to get the last of the cool air in the morning and exhaust what you can in the late evening:
*My personal experience with electronics in the attic itself is that they have a bad habit of melting or frying the transistor. And my personal experience with attic fans is that they have a bad habit of breaking and create another hole in the roof that exposes the attic to the elements or a potential leak. So when I had my roof redone a few years ago, I just had them remove the old unit (it was already broken from a failed bearing) and patched the roof with a new sheet of plywood.