For sanding pen blanks, a 6 inch disc sander also works fine and the discs are less expensive. I bought
this one from HF and it does a great job at squaring the ends of blanks. There is a $55 coupon for it currently in the May 2011 issue of Wood Magazine (and probably other places as well).
For regular square or round blanks, you can use the supplied miter gauge. If the blanks are irregular, I built a little jig that holds an old mandrel shaft. The blank slides onto the shaft, which holds it square to the disc (similar to the one in
this article). It only takes a few seconds to sand the ends down to a shiny brass tube (if you indent your tubes 1/8 inch or so). I can tell by the sound when the brass tube hits the sandpaper. I hook my shop vac up to the sander so there is no mess. All in all, I find the sander to be much nicer than using a pen mill. As an added bonus, it's quick and easy to sand off the corners of blanks to save yourself some turning time, particularly with Tru-stone.
Dave