Both of those invocations would give me pause, because grep is a command that can handle file arguments on its own; in fact it can incorporate knowledge of thos

Both of those invocations would give me pause, because grep is a command that can handle file arguments on its own; in fact it can incorporate knowledge of those filenames into its output quite usefully, so I would generally avoid redirects into grep when I could use it to explicitly, directly, open the files in question.