I’ve been holding back, waiting for one of the more experienced reviewers to take a whack first, but got impatient. So - here it goes.
Bill got my Tunable Brassy Polly to me last Thursday so I’d have it for the SF Bay Area get-together. As per request, it’s a very bright whistle with a two-tone yellow/orange pattern (and bright pink highlights). I told Bill I wanted a whistle I could find in the dark 
and he delivered.
You can tell this is a hand-made whistle - slight irregularities in the paint, the edges of the fingerholes, the cutting angle on the mouthpiece. Not flaws, just evidence of the maker’s hand. Disconcerting if you want jewel-like precision, endearing if you like the hand-made look.
My first thought on playing it was “Wow, this takes a lot of wind!” A few days play has altered that - I’d say it’s a whistle with medium-to-high backpressure that requires a medium amount of air (but good breath support). Until I figured it out, I had a hard time with tunes like “The Ten-Penny Bit” that spend a lot of time in the upper reaches of the second register. Now, though takes a bit more focused attention than a Sweetone, it’s a lot easier to deal with.
How’s it sound? More like a much louder, in-tune, Clarke than anything else that comes to mind; chiffy, not terribly pure, rather woody. And when I say loud, I mean “session volume” but not shrill. Play this and you will be heard. Which, depending on your skills, could be either a good thing or a bad thing - at the SF gathering, I didn’t play it for the few tunes I joined in on.
I got the tunable model, and the tuning is spot-on with the slide about 1/4" out, right where Bill told me it would be. I’d expect the non-tunable models to be equally accurate. The new head design really works well (though I’ve told Bill that an extra 1/8" or so of beak length would be nice) and it’s remarkably resistant to clogging.
Do I like it? At first, I wasn’t sure, but it’s been growing on me steadily. I think several of those who tried it at the gathering had the same initial reaction to either the back-pressure or the sound - if you prefer pure tones or easy blowers, this probably isn’t the whistle for you. (Tony? Limuhead?)
Would I buy it (knowing what I know now)? In a minute. No, it doesn’t compete with the Burkes and Abells (for $15-$25?) - but it’s a very worthy competitor to the Dixon’s and Susatos in its price range.
If you’re looking for the next step up from the cheap whistles, I’d say get one of these and either an Oak or Dixon D (both pure, easy blowers) and you’re pretty well covered.
And much to my surprise, I find myself reaching for this more than any D whistle I own (except my original Polly).