Hi,
I have a rotary blade sharper like this one. It comes with two grains of sandpaper; coarser on one side and finer on the other.
The rotary blade is fixed between two plates that allows you to sharpen one side of the blade at a time, starting with the coarser side of the sharper.
My experience is that you can shape a blade twice or three times, but then its finished for fabric cutting, but can live much longer as a paper cutter.
I think the sharper is helpful when I have forgotten to buy new blades and need a sharp one immediately!
Good Luck!
:)