Summary: This is an excellent product however, I wish canon had made this a standard feature on the 5dMKII body rather than an add on. I am sure even pro photographers use things like this so as to better their composition. Over all this is an excellent product and it helps ease composition especially when you do landscapes.
Summary: A grid focusing screen makes it easy to ensure straight, parallel lines in architectural shooting, as well as level horizons in landscape shots (especially a sunset over water). I bought this screen the day it became available. I keep it on my camera all the time, because the grid lines are very finely etched and don't get in the way when you don't need them. It took me less than a minute to install it.
Summary: I specialize in architecture. Virtually all my pictures are taken with a tripod and the vast majority must have straight verticals. The screen is very helpful. Too bad I could not use the screen I had in the Canon 5D. Neither the screens or the batteries are interchangeable.
Summary: This focusing screen provides cross hatched lines. Extremely useful in line up the horizon (or any straight line in your photo) and as a rule of thirds helper. It has cut down my use of the straightening tool in Lightroom.
Summary: The same as the standard screen, except with a grid. I don't find the grid obtrusive, but it is very useful if you need to line up a horizon, verticals, etc. I used the Ee-D grid screen on my original 5D and immediately purchased the Eg-D for my new 5D MK II. I'm giving 4 vs. 5 stars because I see no reason why the price of 5D MK II accessories should be so much more than those for the original 5D. This seems true across the board for accessories.
Summary: Easy to install, comes with tweezers to ease with the installation and to avoid touching. I have never been good at getting a level horizon, this product solves the issue. Provides light non distracting grid lines that enables you never to be able to get horizontal and vertical lines wrong.
Pros: Cannot Do Without, Easy To Use, Improves Product Function
Summary: Its better than the standard screen in the 6D.Just be careful not to get any dust specs on it when putting it in the cam. Is a little tricky but has clear instructions a monkey could follow. Helps composure.