The pens can be effective too. I've got a set of Spot-Tone pens, and they work better for me than the dies and a brush, but that has more to do with me,than them.
Ditto. I have much better luck with the pens, even on toned prints. I have the Marshalls set, and find that the colored dyes are really difficult. Trying to match those things to the tone of the prints usually ends up looking worse than if I had just used the plain colored one. I had an ancient bottle of Spottone which I liked way better than the Marshalls, but sadly I dropped it on the floor and it broke.
I think the idea isn't to match exactly the tone, but just to obscure the dustspot (at viewing distance) so that your eye doesn't automatically go to the white spot on the print.