I haven't tried it, but the Carlton "File-o-Plate" looks simple and efficient ... plus they didn't try the compromizes of a "one size fits all" solution.
I've lost the url, so uploaded my file copy of the pdf from the Carlton website ...
Otherwise the Husky file guide with the plasitc rollers is pretty good.
The Oregon fileguide blocks your vision ... makes you feel like you're trying to sharpen a cutter with a blindfolder on--in which case you're better off with just a naked file.