I’m very very curious about the thumb hole as well! I’ve never heard of this being used on a whistle before, and I’m curious about more details of it.
…and greenspiderweb, it needn’t be brass to do damage to a tooth, for sure! I bumped a Goldie low F while I was playing it and it chipped one of my top front teeth, one of the big two right in the front, the left one! Luckily it’s such small chip it isn’t noticeable unless one looks very closely, still, whistles can be dangerous! I agree, Chieftain Gold probably would have taken off the whole tooth!
I have not experimented with it on low whistles, but I think it would work. It does not affect tuning. The tone can change a bit, with getting lower volume you may get a bit of noise too, depending on how it is used, so you could generate a tone with less volume and less purity.
But I really prefer a thumb hole for C natural on low whistles. That is why I never considered an octave hole further up the tube. I find the C nat thumb hole more important on low whistles. On my high whistles the cross-fingered C nat is strong enough, but on low whistles the thumb hole helps a lot.
I’ve got a thumb hole for F nat on one of my Goldie high D whistle and also on my Goldie G whistle (Bb hole). Both work really well, feel in a natural position and don’t interfere with the tone of the whistle at all.