With 6H30 tubes, UltraSonic Rx and HAL-O III both will effectively and efficiently reduce microphonics and microvibrational distortion, bringing out more of the true nature of the tubes, component, and source music. Both will reduce or eliminate any glare, harshness, dislinearity caused by microphonics, bring about a quieter background with less fuzzy dynamics, truer tonal qualities and texture, better focused soundstage and imaging, more lifelike vitality to the music.
Subtle sonic differences between the two dampers will vary somewhat from one system to another and are subject to personal taste/preference, with neither being inherently superior to the other sonically; they are both basically sonically inert, just subtracting distortion from the tubes. By audition, one person's comparative results might not be the same and could be just the opposite with someone else's system. Regardless, you'll be present at the same concert and have pretty good seats with either.
Herbie's Audio Lab