It was Victor Khomenko of Balanced Audio Technology who first introduced the 6H30 to the audiophile world being that he is from the mother land of the tube and knew it well.
Yes, that tube was designed for maximum longevity and reliability for space and military applications.
In terms of sonics of that tube? It does its job, the BAT gear with that tube sounded richly textured in harmonics with a slight tilt to the darker side of neutral which bodes well with many speakers, rooms and music genres.
It just works, no need to look for all the "cliché" replacements.