My AAA office gave it to me when I went for my TripTik and accompanying Bag o Stuff. The girl drove to Orlando all the time and was real happy and informative about the drive and everything Disney/Uni. I thought at the time that Orlando should hire her for its Convention & Visitors organization.
It isn't really helpful at MK at all. It's more walking than just taking the tram.
If you arrive early to Epcot, it's not very helpful there. It is closer in the afternoon, though.
AK is a toss up. I might use one there.
I don't remember MGM.
Like someone said, you can get them cheap on eBay. I know I could get one for $5 and it would last all year...and I don't even bother. I don't think it's worth the trouble of taking it out, lol.
I still love AAA, though.