I used my Vista HcX for car navigation and it was OK. But when I bought a Nuvi 760 (The 770 has European maps, both have North American maps.) it blew the HcX away. More detail, easier to read screen, and the voice feature allows me to keep my eyes on the road more often.
....but it's not really that small. I would not want to backpack with it and recharging the built in battery in the field would not be easy.