Most of what I play is in the key of C, some in G, some in D, not many others keys, except maybe a Bb.
I cross finger mostly, but I’m not averse to half holing, if needs be.
Mainly old rock/pop tunes with some nice ballads, very little Trad Irish for me.
(I know these forums are mainly Trad Irish, but you don’t have to play it.) 
Because G tunes don’t necessarily sit between one G and the next like a simple scale (e.g. G A B C D E F# G), but more typically extend below and above (e.g. D E F# G A B C D E F# G A B), by which time you’re looking at perfect D whistle range.
Ahhh! That makes sense. Thank you, Peter.
I had to nip into town today anyway, so I picked up some blu-tack while I was there. I reckon that’s less likely to leave a grotty residue. Gotta be worth 99p to not have irate neighbours banging on the door 
Thanks again to everyone for their welcomes, insights, and advice. I look forward to learning more from you all 
Quick nomenclature question:
Bell note - is that the lowest note on any given whistle?
I did a search, but couldn’t find the answer.
Yes, all holes closed.
Brilliant! Thank you.
Good point, while the D Irish flute, D uilleann chanter, and Low D whistle are all Concert Pitch the High D whistle plays one octave higher.
Thanks Richard. I didn’t know about the flute and chanter.
I must say, I am having fun with these two whistles. I don’t expect to be amassing a great collection of them (I already have several other instruments), but there’s a definite risk a low F and low D might join the array next year.
I had a quick chat via email with Yasmin at Dixon’s, about the difference in responsiveness of the two whistles. She suggested I try swapping the heads around, and see if the characteristics swap over too.
I took her advice, and the A whistle was just as lively as before. No significant change on the other either. After a little more playing around with the Bb, trying to figure out why I wasn’t getting the same responsiveness, I discovered it’s just a little more fussy over which angle the whistle is held at (or I’m naturally holding them slightly differently).
Once that’s corrected, it becomes a lot more nimble. So it was purely operator error after all, although they do both seem slightly better behaved with the heads on this way for some reason. That might just be my improved awareness though. Either way, problem solved! More than that, with a little angle and embouchure management, I can actually play “all fingers down” as loud, or even slightly louder, in the lower register than the upper, which will make for better dynamics. It’s gonna take a little more work on my part to be consistent though.
Had fun today, playing tunes out of a clarinet songbook, on a Bb whistle with C fingering. I really like the “capo” approach to this instrument.