I don't know if I'd feel safe in one of those.
Suppose it lost its balance or one of the feet became stuck? Some people might have a problem with motion sickness, if it rocks back and forth constantly as it walks.
I don't know how well this works, but there's a motorized all-terrain high impact plastic wheelchair listed here, the SeeKer 2. SeeKer 1 isn't motorized, but can go lots of places too, as long as one has the physical strength to power it. They're supposed to work in sand, snow, mud, on rocky terrain and in the woods and high grass.
The price isn't listed, so I guess that means that most of us can't afford it without help.