They're a plated bullet, better than Berry's or most of the other plated varieties. I've shot thousands of Xtreme bullets in 40S&W and except for the occasional tumble when they hit velocities over 1000 have proven to be very accurate. I know several remanufactured ammunition makers that use xtreme bullets with little complaints.
I've used Berry's, Ranier and Zero along with Xtreme. I pretty much use Xtreme now exclusively. I don't know if I'd rate the quality better than Berry's, but the cost sure is better.