I tried the JJ and the Full Music 300B/n mesh plate. The Full Music are really nice! JJs tend to be a bit 'edgy', the Full Music sound really smooth and natural to my ears. In end-to-end measurements (i.e. measuring the speaker output with a microphone rather than the amp output), I also noticed differences in the distribution of harmonics. Specifically, the Full Music tended to be dominated by 2nd harmonic, whereas, the harmonic structure of the JJ tubes varied more with frequency - sometimes the 3rd harmonic being higher in magnitude than the 2nd.
The Full Music tubes tend to run around $300/pair on [THAT AUCTION SITE]. The pair I had went back to the vendor, however. One of the tubes had issues with hot spots. Even at 390 V, 65 mA bias the plate on one of the tubes would develop cherry red spots. At 70 mA the spots were quite red, and the tube seemed to want to run away thermally. So be a bit careful and order from someone with a return policy.