They work well. As diggin' said, don't use them on any find with significant value because there is a level of abrasiveness.
With the 4 pencil set, the ones I use the most have the sharpened pencil ends as opposed to the steel wool and scalpel ones. They work excellent for bringing out dates or lettering. Be extra careful if you using the scalpel one, it will scratch very easily.
Take your time when using them. Common date corroded old wheaties work well to practice on.