Cleaning primer pockets of fired cases is part of the ritual of preparing accurate, reliable reloads.
RCBS sells a $15 Primer Pocket Brush Combo (Part #9574) for this purpose, consisting of a threaded handle and two threaded stainless steel wire brushes for each primer pocket size. It is the first tool in the following photo:
The second tool shown is Lee’s $2 Primer Pocket Cleaner (Part #90101). It is just a small blued steel cylinder with a squared-off blade on one side for small primer pockets and on the other side for large ones.
The following picture shows eight large-primer cases. The left two have not been cleaned, showing the importance of this step of brass preparation. The top three were cleaned with two twists of the RCBS tool, and the bottom three with two twists of the Lee tool. I thought the RCBS would be more comfortable and easy to use, but after prepping a batch of brass I became much more concerned about what it was doing to my primer pockets: As you can see the steel brushes leave noticeable gouges in the brass. In contrast, the Lee tool keeps the pocket face square and relatively unscathed.
I can’t see any good coming of marring primer pockets to this degree. Especially over repeated uses the RCBS brush is removing measurable amounts of brass, and if you didn’t need it the first time it will almost certainly be needed on subsequent cleanings since the primer pocket floor is no longer flat enough for a tool like Lee’s to make full contact. Therefore I recommend against the RCBS tool. Lee’s much cheaper tool is a perfectly functional solution to primer pocket cleaning.