So here goes.I have had the Zoo Med Hygrotherm for about a week. I use it in conjunction with the Zoo Med Repti-Fogger and a large Ultratherm heat pad. I have a 55g tank, and the Hygrotherm was $69 with free shipping from Petco.
Photo of it set up with my tat:
First pic the controller up on the wall (little green screen) and the main unit on the window ledge, second pic shows the main unit which the heat element and humidity element plug into, which plugs into the wall and that the sensor and controller come off of. Third pic is my tat with the controller up on the wall where you program all the settings.
So you plug it into the wall. Then you have one plug for your heater and one for your humidifier, and it will turn these on and off as needed to keep your conditions just right. Then you run the little sensor into the tank. And then you program your settings (not necessarily in that order!). My tank is set to 84 degrees and 80% RH since it is on the warm side of the tat. It has been keeping the conditions pretty much perfect since I started using it. The sensor is very accurate when put beside a calibrated hygrometer/thermometer unit that I already had, within 1 degree temperature and 2% on the humidity side.
It has some nice features such as an alarm which will flash if your conditions go far enough out of spec. and also a night temp. drop feature where you can program the temperature to go down to simulate nighttime conditions in the wild.
So the only thing I can't speak to at this point is it's longevity since I've only had it a short time, but I am very, very happy with the performance thus far. It really takes the guesswork out of maintaining the right heat/humidity balance in the crabitat and for me, makes me feel much better especially with exotics like Straws who are sensitive to drastic changes in conditions.
I'll be happy to answer any questions, please pardon me if I don't get back here immediately because we're going though a family illness situation right now and I'm a little run off my feet between a sick husband and two little kiddos
I do wish it had two or ideally three plugs for heaters because I'd like to have one for my Ultratherm, one for my day lamp and one for my night lamp. But I just use a timer for the lamps and the Hygrotherm adjusts the heat by turning off/on the Ultratherm. But I guess when I think about it, I want the day lamp on for the UV (just in case crabs need it) so the best thing for it to be turning on and off is the Ultratherm and that's what is plugged into it. I really don't need the night lamp at all, it's just there for my son to be able to see the crabs because they are really fun to watch at night when they're wreaking havoc 
