It's even useful well into Hardmode, as fewer Hardmode enemies will attack you, and it grants increased life regeneration to give a speedy recovery. It shouldn't be used as a main armor set for Hardmode, however, due to its low defense. It should be used to assist you in mining the Hardmode ores to acquire some decent armor, as its set bonus will protect you from harrassment whilst you mine.
The headpiece for this set appears to be the sprite for the Spectre Hood, only slightly altered and reskinned.
Despite being classed as a "late-pre-hardmode" set, this set is fairly easy to get, and can be made relatively early in-game, as long as a Blood moon has occured in order to get the Phantom Souls needed.
For this reason, this armor set is generally considered a little overpowered.