Hello!
A tin whistle can be turned into a slide whistle thanks to a sliding fipple.
It’s a bit like the tremolo bar of an electric guitar.
Here’s the thing in action:
https://youtu.be/IMwqJv6hB-A
Very interesting! I love seeing little innovations like this. Is this a whistle of your own design?
I can imagine that if the slide were fixed to stop at a certain length, it could also be used to very easily play chromatics.
It kind of reminds me more of a plunger for a trumpet or a trombone. At least that seemed to be what the musician in the video was emulating any way.
Yes, it’s of my own design.
Adding a flat to each note is very easy, you’ve just to make a very little move.
There is no stop, so if you slide too much down it simply goes off… and this can be funny!
Jam in Ab with the fipple alone:
https://youtu.be/XUMEdxl7TSs
I like to put the fipple deep in my mouth so it bends the note and change the sound (as we can do it with a blues harp) but this is another thing…
The performance aspect of your invention certainly helps to put the spotlight on you. Even in those few clips people are seemingly “bedazzled” by this odd instrument.
Quite a showpiece there. 
There have been many musicians that have tried to get people to pay attention by external means.. (Dressing weird, Screaming at the audience, inciting emotions, you name it someones done it.) That little thing you got there does the trick quite nice!
Groovy! As you mention on your website, it’s the whistle version of Robert Dick’s Glissando Headjoint (for flute). I also like your adjustable finger hole design.
Chapeau!
I think Mr Poulin’s whistlesmithy needs to be added to the WMD (if it hasn’t already – I didn’t find his name listed).
I also make whistles with tunable holes (with a ring system that produces flats).
Here’s the notice (I’m sorry if it’s in french but I’m from France):
http://www.jeanpierrepoulin.com/PDF/Multigammes.pdf
From page 7 there is more drawings and notes than text anyhow!