Actually it is, because the low B's fundamental B0@~30.8Hz is below the ability of most gear to accurately reproduce, and a lot of people's hearing. Try it with heavy flats and a mute to damp overtones and note the precipitous roll-off of the actual, true note. Even E1, the traditional low end, is often problematic @~41.2Hz.
True bass instrumentation is about the low fundamental frequencies, and that's not what you're hearing with those "extra notes" on a five with rounds, but higher overtones -- "bass guitar" sound -- for which I personally have no use except as effects or second-track bass.
We've been through this before, and I'm not inclined to do it again. The physics support the premise and (just barely!) the classical bass tonal range.
There are other reasons to use or not use a five, but they're all in the not-use column for me except for second-track stuff. You may feel differently.
your Uncle touched you in the no-no spot with his 5 string when you were a kid, didn't he? C'mon, just let it out. Let it out. :drphil:

