As I sell the NS1 I can't provide you unbiased feedback, but I can tell you that it does capture altitude using a GPS receiver. The GPS altitude is very accurate, unlike barometric pressure based altitude.
I've personally had an NS1 on my mountain sled, either a prototype or a production model, for 4 years now. I've rolled the sled a ton of times, and I don't even bother to remove the display from the mount before I do so.
My brother is the only person I know who's managed to break an NS1, but he hit a tree to do so. Even then he only broke a couple parts of the mount, and the display and vehicle interface was fine. He rode it the rest of the trip with a bit of jerry-rigging.
The navigation features are especially useful if you're exploring new territory. Overlaying aerial imagery on topographic contour lines is a receipe for finding untracked snow, and the NS1 is designed to do this.