I assume you speak of the newer, high D flute, by Sweetheart, the Professional model.
I have one, conical bore and all, and although it is not something I play every day, without question it’s really good, and it beats the daylights out of any similar whistle, no doubt. Indeed, if whistlers knew about it, there could be fewer whistlers, as they’d be playing one of these, instead.
However, as a cautionary note, if you’re going to spend any amount of time playing it, remember that it is well into, and even beyond, piccolo range, so either limit the time you play it, or use hearing protection. Yeah, it gets right up there, so be careful.
Non-tunable beyond embouchure and cork adjustment, cylindrical bore, round embouchure, but it has stronger bottom register than a traditional Bb marching fife.
If you want a “D” fife that is tunable and has a LOUD usable range from the first on up to wheresover you can take it, get one of Skip Healey’s. You can even get it with 10 holes (fully chromatic) Drive your wife, dogs and the neighbors crazy! They will beg you to go back to a whistle.