Been running a DT steady for 6 years now, just finished replacing the ball joints for the third time, this is with regular maintenance and oiling, not faulting the unit but I think given the nature of the joints, you will have to replace them periodically. Properly set up (equal free movement on both joints), the unit does its job. I also don't believe any head steady unit can be expected to minimize vibes unless equipped with the suspension spring (which mine is).
All that said, I just placed an order for one of Jim Comstock's units, it's much more robust (sealed and larger heim joints), and though pricey I figured I've put so much money into my suspension and front end that it's worth it