Tung Sol 6550 NOS vs Grove Tube 6550A NOS

I'm using Tung Sol black plate 3 holes 6550 NOS for my ARC Ref 6 per-amp,  I'm using this about 1500 hours and want to get a new tube a few months later.   As know it's hard to find good condition Tung Sol black plate 6550 NOS now (even if you can find, price is very expensive).  But i saw some Grove Tube 6550A NOS are offering in the market, I know nothing about Grove Tube 6550 NOS, here are my questions:

1) I want to know how's the sound quality of Grove Tube 6550A NOS?   How's the sound quality compare to Ting Sol 6550 black plate NOS?  

2) What is the reasonable market price of a  Grove Tube 6550A NOS now?

3) I find information that  Groove Tubes is not a tube manufacturer.  May I know who produce this tube and produce in which country? 

Thanks!