The histogram is very small. I wish there was a way to resize it like the zoom box.
In photo mode you either have to use canon's histogram (image is tiny) or deal with the small ML overlay one. They do not play together. If you're not in liveview the overlays pop up on review and push out canon info screens.
Overlays don't seem to show up in normal play mode except as a bug: i.e. some pictures have crop marks in the preview image.