Get both the doffing brush and tool. The doffing/cleaning brush serves two purposes. When you are ready to pull your newly carded batt off the carding machine, use a doffing tool along the metal strip to break the fibers. Next, pull the batt off the drum using the doffing brush. When you have your batt off the drum, you can use the doffing brush to clean any fibers that did not come off the drum.
The doffing tool is used to pull the batt off the drum once you have finished carding. Just slip it along the pick strip an inch at a time to get your batt separated. The end is blunted to prevent sticking yourself or damaging the pick strip. The shorter length makes it easy to use.