NONE of them are concerned with pure intonation

If you don't tune the sympathetic strings to pure intervals they don't work. The difference in power is enormous.

If the thirds on a mouth organ are tuned to equally tempered pitches it sounds crappy and feeble. Which is why they aren't made that way.


one of the things that can really screw up a relative beginning student is to lumber them with a bunch of unnecessary historical minutiae before they fully understand the basics

You and josepp are the ones introducing unnecessary theoretical clutter. The idea of closing the circle of fifths by 12-tone equal temperament has exactly as much rationale in traditional music as closing it by 19-tone, 31-tone or 53-tone ET, i.e. none whatever. For folk idioms, you simply don't need to know ET ever existed. It's a piece of 19th century art music theory which is great for understanding Wagner, Schoenberg and Duke Ellington, and completely pointless for anything far outside that range of idioms. (I just flipped through Rameau's "Treatise on Harmony" of 1722, the most influential music theory book of the 18th century; no mention of it there, which is not surprising since the first piece of music to use it in a nontrivial way wasn't written till 100 years later). It doesn't make you play any better, doesn't add any understanding of the music you're dealing with, and it seems it blocks off your perceptions so you can't even hear the sound of a mouth organ right.

On the other hand it does make some sense for people to understand ET if they're playing instruments that are such a disastrous misfit to traditional melody as the guitar - simply so they'll know when to just STFU with the out-of-tune noises that blur the overall harmony.