Analogue hygrometers are fine as they don't need to be 100% accurate as long as they don't stick (mine got stuck at 55%). A stick on thermometer is sensitive but 1cm from the bottom on the hot side is equal to around 5-7 deg F depending on ambient temp in the room. At 2cm from the bottom it could be off by as much as 12 deg F. Assuming you use an undertank heating pad. A digital thermometer can have the probe against the bottom and will be more accurate to the real temperature, and if you get a digital thermometer you might as well get one with a hygrometer.