I have the GP-E2 on the 5DIII and am pleased with its performance. My only regret concerns the Map Utility software, specifically that if I go away for, say, three weeks, the best I can do is twenty-one separate plots of my route for each day. The program needs to be modified so that I can select multiple days and therefore display my entire route for the three weeks. It might be possible to do this with a lot of stuffing around and manually editing the files, but I don't have the time. Canon, are you listening?