I'm running some CAT6 cable and want to have a surface mount box on the wall so that I can easily plug thing in. I see there are keystone boxes out there, good. One option is to use RJ45 keystone ...

Do you mean inline, to extend the reach, or do you mean multiple ports on a single cable, to connect more than one device? If the former, yes. If the latter, no. edit, because someone will point this ...