I agree about the Granberg. It is especially clever in the way it will match all the cutters to the same length. Doing that by hand requires a constant measuring and re-measuring with a calipers, the Granberg does it automatically for each cutter.
However, it is difficult to get a Granberg in your pocket to take with you in the field.
After about 4-5 sharpenings with the roller guides, there will be variations in the lengths of the cutters. At that point, a Granberg will clean up the lengths and angles. However, it does not provide a progressive raker depth, for that you have to go back to the roller guide raker plate.
It seems to me that the possession of both the roller guide and the Granberg provide a complete filing system for all situations.