You really need to check these units out in bright sunlight. The transreflective displays completely blow away anything any smartphone has for bright sunlight conditions. (I run the mobility section of a proof-of-concept lab and receive a half dozen new, sample, and prototype smartphones and tablets every month, --so I pretty much know every kind of display on every smartphone made). At least you should google what transreflective displays are. Any criticism of transreflective displays would refer to low light (dusk or indoor) where you're not quite ready to turn on its backlight. And those are accurate criticisms.

And I do use the GPS for my primary mapping device. As to why I use it for 10 hours, --I would turn the question around and ask why not. We ride long and complicated routes with dozens to many dozens of turns every day. I wouldn't want to have to turn my GPS back on again at every decision point. And we frequently encounter unmarked country intersections. The map folks are sometimes stumped while my GPS shows a highlighted route on a moving map display. Often the "map" folks look to me to resolve uncertainties. And when I ride sweep for a large group including kids I need to stay exactly on the planned route. These are pre-planned routes that are either printed out as paper pages (maybe 20 pages per day) or waypoints uploaded to GPS devices like my GPSMap60Cx. These things are actually very useful for long tours.