I have learned to do a quite good setup thanks to these. I had my guitars setup by a "professional" luthier, and he missed the crucial point - the nut. I have set up my two Yamaha acoustics with these, and they feel so much better, and the intonation at the first fret is finally good.
Oh and a tip for you: be VERY careful when filing the nut, especially on high gloss polyurethane stuff, such as USA Fender. Protect the headstock by all means and protect it well, or you might easily stick the file into it. Learned it the hard way.
All in all, a great little investment that will save you time and money, teach you an important new skill which you could actually charge to other players.