Recently, I came upon an almost NOS pair of black glass Ken-Rad 2A3 for a great price, so I ended up buying them. They have about 150 hrs on them by the prior owner and are essentially burned in.
How do they compare to my EML 2A3s? Well, they don't have as extended highs or bass and are slightly less resolving but the mid-range is wonderful. They are very musical. Now I can see what all the NOS supporters are talking about. Ultimately, I still prefer the EML but if you have the opportunity to get some reasonably priced NOS tubes you may be surprised.