Humidifier question

[Big Maduro]

Now that I'm home it's a little easier to surf than my phone. Heartfeld has just what I think I want. It's an aluminum humidifier that replaces the plastic one that comes with some humidors. It's 6.5 x 2.5 x 7/8 holds up to 4oz of 70% beads. One more thing if I may. Is one hygrometer enough? Would it go in the top shelf? My humi is about 1440 ci.