The quality of the focusing screen is equivalent to 100% of the original that comes with the camera. The lines help you align very, even though the viewfinder of the 5D II is actually very big and bright and per se is well suited for cut selection. Why can not extradite this ground glass than the original with the camera, is beyond me. There is really no reason to take this to use the original focusing screen.
The conversion should thanks Video instructions (eg on YouTube) be feasible for everyone. Who then is anxious, this can usually be put in the photo shop.
Small drawbacks: in night scenes or very dark subjects, the lines are difficult to come recognizable and unfortunately the division is not really 1/3 rule accordingly.