Both the Sovtek and Electro Harmonix are made in the same factory, same tube. If anything might change the tone, it would perhaps be the gold plate to improve contact. Source: Upscale Audio. They also match and offer cryo at a premium (as does Cryoset) .
I would be interested if any opinions, heard difference, to include cryo vs non treated. Victor at BAT, says he doesn't believe it the treatment but does not say why. As for matching, in my VK50SE, Victor does not seem concerned about more then 10% or 15% mismatches, as the balanced preamp "blends nicely" the differences. Who would have thought. Last thought on cryo, I buy 7591A EH from Cryoset, and there is a noticeable difference for that power tube.
Final thought on the new manufacturer and base knowledge so far from members, "extreme precision matching" may be a waste of money on the 6H30 depending on the equipment. Noise, microphonics, and grid current, are more important according to Victor.