Grant Fidelity provided a pair of sample Premium Grade A 300B-Z to TNT-Audio.com. Reviewer Geoff Husband says:

“If you are looking for a more even performance then the three candidates are the KR’s, the Shuguang and WE re-issues. The latter are very expensive, and to my mind offer nothing over the other two. The Shuguang and KR sound very similar, but the Shuguang build quality is inferior to the KR’s. The decision then comes down to availability and price – the KR’s are more expensive but beautifully made, but not always available. The Shuguang on the other hand are less well made, but at least as good sonically and, depending on market, cheaper.”

Read full review here: http://www.tnt-audio.com/accessories/shuguang_treasures_300b_e.html