In expressing disdain for the, hm, 'squiggle', David sets big store by several heads of criticism, first by claiming it's a rank outsider, among tunings of Bach's day. But if that is true, and Bach's writing for all keys inclusive and without exception in The Well-Tempered Clavichord (note that 'The' with which the title opens, it isn't 'A') was not some purely abstract notion whose day could never come, what exactly was the point of this apparently-pointed Title? That IT was no better than any other already-available tuning presumably, (and also assuming that IT - the entire body of pieces in the books - had no hope of being really playable on real instruments, ever, in Bach's mind). That seems to be exactly what David prefers, over the 'squiggle'. He is explicitly resentful of what's becoming a status for the Lehmann conjecture that a squiggle could be a Bach denotation for any preference on his (Bach's) almighty part. That's the point. Being an outsider - and it's a possibility. An almighty tease, just on account of WHO might have denoted it, no matter in what way.
The other great store he relies on is the upside-downness in the 'squiggle' 's interpretation. Leonardo was left-handed, as proved by his shading-strokes. It's trivially silly to imagine he wrote mirrorwise as 'code' to protect any heresies he might write. Decoding by a mirror would be too easy. So why? Simple left-handedness : writing backwards is easier for a lefty - one of genius anyway - less self-cramping. Was Bach a genius? Well, he wrote music involving theme-stretch, squeeze, backwards and, hm, upside- down. Never mind in five voices. And puzzle-canons (yet, extended ones). He thought these ways at breakfast, elevenses and supper, and not just occasionally, by the year. This objection is too trivial to bother much with, any number of reasons might account for it with just the meaning proposed. More cogent is to wonder why and when the 'squiggle' was added (as it was, crowded into the top where there's no space for it, less-tidily than the entire rest of this carefully-constructed and executed formal page, though probably by the same penman). But David will be happy if this objection will pass as a discrediter, has no interest otherwise.
As for myself (no educated background in tuning whatever), I take Lehmann's word at face when he describes his tuning as beginning from Valotti, which he expects all electronic aids to offer. Scala gives Valotti 2 entries, and says the first is called Valotti-Young (I think), adding it's sometimes called Valotti-Tartini. Applied to Kreisleriana, it sounds pretty good, as good as the 'squiggle' anyrate. Presumably Schumann would know it, though where he'd rank it who knows.
The last post on the page you link has David lifting the lid on why he's so coy about his tuning's details. He considers it his main performer's property (forget exact name right now), with possible rights-money swinging off recordings.
