The reason people consider the manuals an upgrade is that they don't disingauge when you slip back down a hill. Once they're locked, they're locked. Auto hubs are designed to disingauge when you roll back (part of the unlocking feature described on your sun-visor). Great when you don't want to get out of your truck in the mud and snow, bad when you're stuck on the side of a hill and have to get moving forward in 2wd to lock the hubs up again.
With manual hubs, always engage them before you need them. Keeps your boots clean. ;-)