Well, Jack, you're far more savvy than I am when it comes to these blown things. I actually have a Susato tunable whistle. It's loud and proud and very pure in tone (I don't know how else to describe it). It isn't like any other whistle I've tried to play (I'm a crap whistle player so I haven't really investigated anything costing more than a very few quid). What I do know is that Susato whistles are either loved or hated, never actually affectionately indulged.

It's interesting what you say about blending. It's perfectly possible for decent harmonica players (especially when they are playing single reeded instruments, not tremolos) to subtly adjust their tone and pitch in order to blend with what they hear around them. It's fifty per cent about listening and fifty percent about your playing skill. A concertina in the wrong hands can sound like a harmonica without the humanity, but I've known some good players who seem to surmount the difficult-to-blend issue. A lot depends on whether you're at the same pitch as, say, fiddles. Oddly, though whistles generally have, er, fairly "approximate" intonation, they seem to suit the aesthetic of a good Irish session perfectly. Discuss!