I was out on a Morris day of dance on Saturday, and one ladies side - Old Palace Clog, play all their tunes in C or B-flat, because they have a clarinet in their musical line up.
A lot easier to play on a Bb or C whistle than a D.
quite like Bb and B# there, innit? 
As a piper, I also like the Gen Bb. I also like the idea of your modification. May I ask what you used for the extention and what length, diiameter, and so on. Sounds great. Best, Cyril.
CranberryDog-
I will have to get my calipers back, but I just used brass tubing that fits just inside the Gen. for the “foot” extension, and telescopes in and out to tune it. I used a tube of slightly larger OD (again brass) than the Gen. itself to make a tuning slide. There is a little drop in pitch when it hits the second octave, but if you wnated to play GHB tunes on it, they’d be only an ocatve anyway, so I just pick an octave, and tune it up.
Hope this helps, will let you know about the hole size/placement.
Is there any particular reason why Generation whistles stop at Bb and don’t do A?
Is there any particular reason why Generation whistles stop at Bb and don’t do A?
For some time they went down to G, the lowest whistle available at the time. Some time later both Hohner and Camac (we’re talking seventies here) made whistles going below B flat. I don’t think there was much call for them at all and that could explain why they were disbanded.
If you’re looking for stuff to play in Bflat, get Heathery Breeze by Matt Molloy. He plays lots of stuff on the Bflat flute on that. I think there are a couple of other fluters who like low flutes too, but I can’t bring them to mind.
Isn’t Bb also the fundamental frequency of the Universe?
Shhh!!!
If they don’t know why Bb, they aren’t ready to know that…
The most obvious reason for a Bb, of course, is that Babes often sing in Bb. Whle the fiddler is apologizing for his inability to capo his violin, the prepared single male whistler whips out his Bb tooter and says “I can help you darlin’”.
Guys with Bb whistles are chick magnets.
Doc
if you’re gonna use that stuff open a window, ya need ventilation 
Too..many…obvious…jokes…must…restrain…self… 
Kevin Crawford comes to mind, i think McGoldrick has recorded with a Bb flute also.
To Bb or not to Bb?
I never had much trouble with the question. With a new Generation Bb only $6 and 3-5 days delivery away, I bought my first Bb (many, many moons ago) before I could think about it too much 
Well, I do like my Bb (a Generation in brass). Only thing I don’t like is that I can drop a paperclip down the fipple of my Acorn D, but not the Bb, so the only way to avoid annoying people with my awful playing is to blow across the window, which is highly unsatisfying.
It does sound nice, though. It kind of has a nice squawk to it. I can’t play nearly as well as on the D, but I can’t play the D all that well, either. I’ve only been doing this for 3 weeks now. I’m posessed. I’m even learning to ride my bicycle no-handed so I can practice on my way to work (I bicycle commute).
be careful
they’ll get stuck in the spokes
I used to play with an Irish guitarist who was more used to playing as a soloist. I’d let him start and figure out the key and grab the appropriate whistle. I started getting used to what keys he played in and we’d start together, sometimes in Bb. One time he tuned up his guitar and suddenly, we were in B. I told him that we had originally been playing the tune in Bb but I could do it however he wanted. He paused for a moment and said, “Just give me a B, I’ll flatten it meself!” 
The purpose of Bb whistles are to make A# ones unnecessary…
John Skelton plays a Bb flute, too. Lots of these fellas do.
The fact is there are a number of recordings in Bb, and on
various instruments, e.g. guitar. So if you wish to play along/
learn the tune, etc, the Bb whistle comes in handy.