JJ Tesla EL34 Blue

Does anyone have any experience with the JJ EL34 Blue tubes? It is claimed to have tighter bass and more extension than the regular EL34s without compromising mid-range and HF. Thoughts?
Who makes those claims? So far as I know the only difference is the blue glass which some seem to like. Actually I prefer the red filiments and blue gas lights of normal tubes.
It is true that these tubes are E34L, which do have more bass, extension, and a bit more power than EL34. They are higher voltage than the typical EL34. JJ also makes them in clear glass, as well as red. My favorite EL34 in the market, although many feel the Svetlana is tops. It depends on your tastes.