I have the Shuguang Treasure 6SN7s on my Don Sachs preamp. Don says in his website that these simply walk away from the holy grail NOS tubes. That's quite a statement.
Obviously this is not the case with all NOS tubes...as a lot of the culture that made these tubes is gone forever.
My main issue is you can no longer get the Treasure variant of this tube from Shuguang (luckily I bought an extra set). You can no longer by the WE version anymore either. Psvane are hard to come by too. Now we have the Linlai.
What is up with the availability of new production tubes from the east? Not a good sign. Make a good product and keep improving it and keep making it.