Overview: I bought this with my 5d mk3. So far I have nothing to complain about in terms of the device itself. It works as intended and locks my GPS position on every shot. I've used it on a couple of hour long walks last week and haven't had any issues with it or with the battery life. When I got home and uploaded my photos to iPhoto, I was happy to see that all of my images were correctly geotagged with exact location and direction. compared to other manufacturers like Nikon, takes place in the hot shoe. Conclusion: Overall I am very satisfied with the GP-E2. It gets the job done for what you need. Having said that, I think Canon should have originally integrated GPS into the 5d mk3. It's actually ridiculous to pay that much for a camera without built-in GPS, especially when they've just announced a new low-end full-frame 6D camera with built-in GPS and Wi-Fi. Also, it would be nice if they offered some sort of GPS unit/battery pack instead of just offering a GPS that takes up space in the hot shoe.