I have had the little Canon GPS GP-E2 for a little over a month now, used it exclusively with my Canon 5D Mark III.  Tonight I realized it works perfectly with my Canon t4i too.   In both cameras you turn it on, slide it into the hot shoe and as soon as it has a satellite lock, and it often gets that lock quickly, it feeds the camera your precise location and altitude, UTC time too.  This can all be displayed on the LCD screen under the GPS Device Setting screen.  It also works  with the Canon 1Dx and 7D Cameras(needs USB cable connection when used with Canon 7D).  Can be used with any camera via the logging function but not recommended for use that way as there are cheaper options including using an app on your smartphone. My Original Review of the GP-E2 Unit