Good marketing on the part of PSVane, however I doubt the quality of these has been improved. I purchased a quad of the preferred series from Vivatubes and within 6 months (maybe 200 hrs play time) three of the 4 died. Viva didn't honor their one year warranty (in fairness, they did send one replacement for the first but radio silence for the 2 subsequent).
Sound quality was better than the Shuguang's that came with the amp, however if 75% of your products die within a few hundred hours of use, it really doesn't matter hhow good the sound might be. FYI - the cheaper JJ replacements have been going strong without problem.