I know what backpressure is, but I’m not completely sure if it’s something I would really want or need. I’m primarily a flute player (still a novice there), but I do play whistle some. My main whistle is currently a Burke aluminum narrow bore D which basically has no back pressure.
So, what are the main reasons that players want a whistle with backpressure? Does it give some advantage in playing, or is it really just a preference?
Bob
For me, it’s mainly a matter of how much air do you need to play the whistle. More back pressure usually means less air, longer passages played without needing to refill your lungs. I don’t know if there’s an exception to that rule. There are whistles with little back pressure that are plenty loud, so it’s not necessary to have the pressure to generate volume. Back pressure itself doesn’t give me any advantages I can think of.
Personally, I find some whistles fit into a comfort zone where I can play long enough without running out of air balanced against a feeling of being oxygen deprived because I’m not breathing enough. Low air requirement whistles have me exhaling through my nose at times to bleed off CO2. Playing with the feeling that you’d like to ventilate your lungs interferes with concentrating on a tune. So, if you’re feeling light headed because of inhaling a lot too frequently (as in flute in my case) or feeling like you’re suffocating, you want a whistle that finds the middle ground.
If you’re comfortable with playing the flute, you’d probably be happier with a whistle with less back pressure.
Tony
I thought backpressure was the pressure of the air required to make a whistle perform, not the amount of air.
I would think just the opposite is true. As you advance as a flute player, you create more backpressure by getting a more efficient embouchure.
Bob
Yes, I think what Tony is trying to say is that often with a higher backpressure comes a reduced air requirement. (Ie, they are different things, but not independent.)
OK, other than the lower breath volume requirements of most whistles with higher breath pressure, is there any other advantage? Since I mostly play flute, I haven’t found any high whistle that requires too much air. 
Bob
Bob, If you can fill a flute I doubt that the air requirements of any whistle will be an issue for you.
Increased back pressure may also give a bit more ability for expression.
Doc
Whistles with backpressure can give you more expression. Triple tonguing is a lot easier with a whistle that has lots of backpressure.
I’m primarily a euphonium player so I may be in a similar boat with Norseman. The euph requires a lot of air, although probably not as much as flute. When I play my Shaw, which to my reckoning has relatively low back pressure, I have to find creative ways to get rid of the extra air I couldn’t put through the whistle without squeaking. I switched to a Chieftain which also requires a lot of air but I think the higher back pressure allows me to put through a large volume of air faster without jumping octaves and squeaking.
I like whistles with little backpressure, especially Freeman-tweaked Shaws. Plain Shaws have a lot more, but the tweaked ones are about right…
As primarily a Bassoon player i am used to a ton of bacpressure it just doesn’t feel right to play some thing with out it. Yes, I do wish FLutes had Back Pressure.