Hello Tim,
if you have any of the 5 different Mullard 12AX7 revisions, please inspect them visually compared to the so called "new version" and you will find that there is not even a remote similarity.
If you take the tube apart and check the components not visible from the outside, there are even more discrepancies.
All constructional issues that makes a Mullard tube special or better, like the "Philips Blackburn" construction are missing and in the end these copies are still nothing other than a tube "Made In China".
Even if you disregard constructional features, and just compare the electrical specs, you still wind up with a run-of-the-mill Chinese tube. Noise, sound and most of all lifetime are pretty much off.
For Groove Tube's 6L6 version I can add that at least the plate material is NOS stock- GT got it from Charles Whitener, the guy behind Westrex, but there is much more to a real GE tube than the plate material...
Best regards,