I have generally found the AC routes to be so easy to follow that I leave my dedicated GPS home. I do sometimes use my smart phone for directions to a particular stop, service, or attraction.
I have used an etrex for an on/off road tour and it worked out well. Personally though I found it a lot more trouble to program in the route, deal with batteries, and so on than it is worth on most routes especially if you will be on the road only.
I have never used GPS. I like Pete's advise. Use maps, intuition, ask the locals (although they rarely know anything about their own area!), get lost on occasion; it's all part of the adventure. I really think many of us are way too hung up on gadgets and electronics. I'm such a dinosaur that I still don't use my own earphones at the gym or out on a walk, etc!