There has been no harm in doing both IMHO. My testing (RedHat Linux w cPanel) has shown it helps delivery to AOL where the client IP (mail client) is in a portable (aka dial-up) range.
Add the true IP of that the email server is bound to as cPanel grabs the IP4 A record of the webserver. Listed as 'Additional Ip blocks for your domains (IP4)'.
The best of the online SPF record checkers is [kitterman.com ] There are others but they give confusing results (IMHO) and/or false errors. openspf.org has lots of backing docs if you are curious.