Hello Simon,
I use mine a fair amount and when they are sharp and set up correctly they are a pleasure to use.
When I sharpen mine I use a fine needle type file and try to keep a single bevel as near as possible to the original profile.
When the blade is fitted it is just a case of adjusting it back or forth to suit the timber being cut and the size you require to the nearest cutter block you are using.
Make sure you cut the square stock only 1/8" bigger than the size you need.
If you need a copy of the original instruction booklet or a photo of a new blade let me know.
Merlin