I use the plastic bushings for the same reason. Some early pens of mine had darkened ends, caused by sanding tiny bits of steel from the bushings and embedding them in the wood. These days, when I am done turning and ready to start sanding, I switch to the non-stick plastic bushings. Here are a few hints:
* Plastic bushings let you sand the pen blanks from end to end and finish them. That's a good thing, but you must be careful to avoid letting sandpaper wrap around the end and round it over. That would ruin all the hard work you did to match the metal bushing diameter, eh? The important point is that if you accidentally touch a plastic bushing with sandpaper or finish, nothing bad happens.
* The plastic bushings fit inside most pen tubes, which exposes the ends of the pen blanks nicely. They are essentially flush on the thinnest slimline pens, but it doesn't matter.
* Before sanding or finishing, I give the blanks a quick spin on the lathe to make sure the pen blanks are well seated in the plastic bushings with almost no wobble. If they wiggle much, I give the bushings and blanks a few twists to reseat them and test again.
* In addition to sanding, I use the plastic bushings for all pen finishing, whether CA or friction polish.
* After a CA finish, the plastic bushings are much easier to remove from a pen blank than the metal bushings.
* The plastic bushings can leave hard CA rings at the ends of the finished pen blanks. I hold the pen blank vertical against sandpaper on a flat surface to sand it off. Be patient, gentle, and careful.
* CA glue/finish can build up on the plastic bushings. I use a fingernail to pick off the hard CA coating, and the bushings are as good as new. Sometimes I wax the plastic bushings with Renaissance Wax or Johnson's Paste Wax. The wax improves the non-stick feature of the bushings and makes it easier to pick off the CA build-up.
* Buy a spare set of plastic bushings. The plastic bushings are small. They like to hide in the sawdust or get sucked up in your shop vac. More than once I have sifted through the sawdust in the dust separator to fish out a plastic bushing. I have a spare set of plastic bushings just in case, but I have not had to open them yet. Somehow my original set of four plastic bushings have survived for over 70 pens. A miracle perhaps, but trust me, my luck won't hold out.