The Enchanter's Barrier and Bullet Barrier are only 2 among +- 12 items that grant bullet barrier, and are definetely best 2 of them, as they buff you whenever you have barrier.
But no, they are not OP. Unless you're playing backline character (like Vindicta, Geist, Talon, Pocket (though Pocket is on that list for different reason)) who rarely gets shot enough to lose barrier, they are way worse value than armors.