First, I want to say that for the price this is a pretty great deal.
The tone is great - clear with a bit of an edge, barely breathy - with good volume.
I love the tuning slide, I definitely trust the cork on there much more than I trust slides relying on teflon tape (besides, I don't particularly like anything about disposable plastic), and it gives you a lot of tuning range.
There's nearly no back pressure at all, which in my case is a bit of a shame, I do like the back pressure ; that being said most of the range doesn't use all that much air (the B and C# use quite a lot in both octaves, but that's pretty unavoidable)
My main complaint is that the upper octave is quite hard to play in tune as the air requirements are very different from the lower one - the high D requires as much air as the low E or low G, about the same for the high E, and the high A, B, C, C#, D'' need so much air that they sound very sharp no matter how you adjust the tuning. It can be mitigated by careful finger placement but it does make the instrument rather hard to play.
As for the build quality, the aluminium is very roughly brushed on the outside and has some sort of texture on the inside, nothing fancy. The tube's also quite thick, which means it's not the lightest low whistle but at least you don't have to worry much about the metal parts getting dented. The tuning slide has a very thin and somewhat sketchy cork strip, but as I said I'd much rather have that than have to put teflon tape !
As for the head, it is plastic but it's very well finished, there aren't any visible edges anywhere and it's also of a quite high hardness. The block looks like it's removable, but I have to say I didn't take any chances with it yet.
Note that you will need cork&slide grease for the tuning slide, and that the texture inside the whistle clings on dirt and saliva, so you will have to plan your cleaning accordingly.
All in all, a good whistle for the money, with a great sound a very respectable volume, on the louder side for sure. I just wish the upper octave was more in tune !