I don't know what there really is to be disappointed about, its pretty simple. I haven't read the reviews, but I've been using one since summer and I know a bunch of the other guys use it too.
It's literally three steps. Download the app, calibrate overnight using their instructions, stick it in your box. Works through Bluetooth up to 100 ft, if you only use the one step calibration its accurate up to 2.5% like most others, but they offer two point as well for better accuracy. It also keeps a history of temperature and humidity fluctuations down to the hour if you wanted to get really specific. I usually check the app once a week from my couch in the living room (when I remember) while my tupperdore is upstairs in the closet.