Comparatively, I actually found them to be stunningly similar. As in, it just felt the same. It may be that JJ needed a tube to compete with the TS EL34B, and I think they succeeded. To make sure you know that I have an ear for this, the Mesa EL34's that were originally in the amp were absolutely brittle. Prescence, presents, presence! If you like sizzling sizzles, that is your tube!
Some descriptions from Eurotubes:
Power Tube Descriptions
The JJ EL34II prototypes came to us in September of 2014 for testing and we were all amazed that JJ could come up with yet another variant that has it's own sound and distinct place in the already heavily populated EL34 family! The EL34II's are fuller sounding than the standard EL34 but not as "in your face" and aggressive as the JJ E34L. If aggressive, tight and punchy is what you want the E34L is King. The EL34II is a perfect choice for players who love a traditional EL34 sound but need to fill out the low mids and low end without losing any upper mid and high end crunch or definition. They are very warm and sweet sounding