That's not how this process really works, though. ATF has already been directed to move "as close to universal background checks as possible within existing law." No matter how polite comment writers are, their comments are going to be ignored. (Beyond the technical responses that are required as part of the final rule process.) Writing something that is interesting for a clerk to read and preserves all arguments as part of the administrative record is really all that is important.
For example, if I were worried about ATF's feelings, I probably wouldn't start a comment reminding them that the current "engaged in the business" language only exists because of the agency's own bad behavior (including getting an NRA member shot in the head as the result of a raid that had very questionable probable cause), but I maybe did do that.