I also think of Generations as being “normal whistles”. Much of this comes from the fact that when I started playing, in the 1970s, there were only two sorts of whistles available, Generations (in their various keys) and the Clarke C. (Clarkes only came in C.)
Generations vary from whistle to whistle but I would search out the ones that played “best” in my opinion: clear tone, very clear sweet easy 2nd octave, round full low octave, quick response between the octaves, and fairly good tuning between the octaves. Generations nearly always have flat 2nd octaves but very rarely you might come across one that has perfect octaves.
On this forum many people will talk about the ‘dirt’ or whatever that supposedly characterises Generations but the ones I picked out played pure and clear.
Anyhow I think of Generations as being “traditional whistles” with the characteristics which come from having a fairly narrow bore for length (easy 2nd octave etc). They’re free-blowing and of moderate volume.
Back in the 1980s I was dismayed when suddenly many new makers came onto the scene (mostly Americans it seemed) whose goal appeared to be to make a whistle that sounded like a recorder, or sounded like a Native American Flute, or anything other than a whistle. These “neo whistles” tended to have bigger bores, a louder low octave, and a 2nd octave which was not as sweet, sometimes verging on harshness, like you were shouting the high notes rather than singing them. The 2nd octave was also a bit more difficult to produce, and switching octaves was sluggish, not as nimble as on old-school whistles. Most good trad players ignored these and stuck by their trusty Generations (a la Mary Bergin).
Nowadays there are whistles like the Sindt which have all the cherished playing characteristics of a very good vintage Generation.
About the ‘tweaking’, usually even good Generations have a slightly flat 2nd octave and this is cured by packing the head. Mine are packed with wax, I’d never heard of blu-tak until I joined this forum. Another ‘tweak’ that nearly all my whistles have (not only Generations) is that whistles quite often have scales which are a bit off here or there, and this I fix by carving out certain holes.
For example many Generation Ds have good scales save for a flat F#. Why live with it when it’s easy to carve it out?
Some Generations have a good scale save for the note fingered xxxooo being sharp (the note that would be G on a D whistle). Common in the old days to see good players with tape on that note.
My wonderful old Generation C is like that, and I played it with tape on that note for over ten years. One day I said “enough!” and I carved out all of the other holes to bring them up to the pitch of that hole, and also chopped the bottom a tad. The result is a perfectly in-tune whistle that’s served me well over the years, the veteran of many concerts, movie scores, albums, etc etc. You can see me playing it in Patriot Games. It’s the finest whistle of any key at any price I’ve ever played.