I had a MistKing Hygrostat that I ran in my setup for just a few weeks. The problem with the hygrostat is that because it is on "autopilot", sensing the humidity in the cage, you have less control over how often and how much it runs. I found that it ran too often and the cage never got a chance to dry so within just a week or two I had a significant mold/rot problem.
It would probably work really well in a greenhouse environment but in a house with A/C, air currents, etc the hygrostat wasn't really measuring the moisture levels in the cage, it was more measuring the humidity in the air of the house even though the hygrostat was well inside the cage. It was a bit of a catch-22, I wanted good airflow through the screens of my cage to keep my cham healthy but that airflow kept exposing the hygrostat sensor to the less humid air of the rest of the house so the misters would kick on well before the cage environment needed it.
As tempting as it is to go with the Hygrostat and be able to "set it and forget it", you are better off sticking with the MistKing seconds timer and having more direct control that you can easily adjust. Trying to adjust by humidity percentage is a lot harder than just adding or subtracting a few seconds of misting time to the timer (or I'm just not smart enough to figure out how to manage it via humidity percentage...).
[I currently have mine listed on Ebay since it has been sitting a drawer for about a month since I bought and installed a seconds timer. If you really want to give one a try, shoot me a direct message and I'll send you the link to the ebay listing. (I don't want to post it on a main thread and be accused of behaving like a spamboy).]
