Yes, that stands for Super Superuser, which quite frankly makes me want to slap someone, but the fact remains that SuperSU brings some functionality to the table that Superuser doesn't have and you might just want.
Features include an option to temporarily unroot so you can play movies or games that are root-restricted (Blockbuster/Google Play's movie service/etc.). It also works in recovery, which Superuser generally doesn't, and claims to work when Android is not properly booted.
There are several other features that it boasts such as "deep process detection (no more unknowns)" that there doesn't seem to be a whole lot of documentation on.
Whatever you decide to do, make sure to check out the discussion and support thread (located in the description on the Play comments) before attempting to install, and for safety's sake go ahead and make a Nandroid. If you lose root for some reason, you'll want that handy to get your root access back.
Links: Google Play (EVO) | Google Play (web)