I bought this mainly so I can improve my ability to judge slope angles. I "guesstimate" the slope angle, then check it on this to confirm what it really is, that way I can update my "mental" model and hopefully get better to the point where I don't need it anymore.
I've found it gets harder to judge as the slope gets steeper. 30 degrees is fairly easy to judge (for me anyway!), but as you get to 40+ it gets a little harder.
OK, it's not what I'd call cheap, someone suggested I use an iPhone app (e.g. backcountry access free app) to measure slope angle, but do you really want to stop all the time, get out your iPhone, open the app, measure, put your phone back etc etc when you could just lay down your ski pole?
Having the temperature is handy, in this photo it was a nipple hardening -15C (not including wind chill!).
It has an auto power off feature and attaches to any ski pole via a velcro strap. For weight weenies - It's super light, you won't know it's there.