I use a yellow e-trex when I cache. Its dose have a compass on it and it really has a lot of other features in that I don't use. The only thing you really need the cable for is updates to the e-trex. Right now there aren't any so don't worry about the cable unless your Planning on seaching for 20 or more caches at a time, Like some cachers then, yes invest in a cable now. Otherwise wait tell you really need one. I will tell you this much I have only lost singnal a couple times this summer. Do mainly to trees and rocks. Accuracy is general pretty good with it. I've been anywhere from 2ft. to 80ft. off on the caches average is about 30 ft. I think it depends on the unit, The cachers uses to get their cords. So I would say to go for it.
I've found about 300 caches with the one that I have. Good Luck and Safe Caching.