Oaks are decent whistles. I’ve got a couple and they’re almost up there with the top three. Most important thing is to learn how to play, and until you’ve got a few years of playing in, it doesn’t really matter what whistle you use.
I think there is some value in using sheet music to train your brain to hear what’s going on, but even in dance tunes there’s quite a lot that’s simply not notated, and never will be. Airs are much worse, and probably the only thing notation is good for is a rough (very very rough, in a lot of cases) outline of which notes are played, in a general sort of sequence. Timing is never accurate, and more often than not is misleading, too!
I guess I’d say you should probably steer away from books at all for airs, and even the CDs that go with them aren’t necessarily that good either. Better to listen to excellent musicians play the one air they’re completely comfortable than to listen to a bunch of airs that may or may not be that well executed or that familiar to the musician doing the recording.
Another aspect to it is that if you look at most recordings of good traditional irish music, you’ll find that there’s rarely more than a couple slow airs on the recording. This is because playing slow airs well, and convincingly, is hard! Arguably harder than dance music. Don’t assume that because it’s slow it’s easier!
I’d like to point out here that I’m using the term slow air to refer to a particular style or subgenre if you will of melodies to songs and tunes in a similar style, while air refers to all melodies to songs, or pieces in a similar style. Something like Si Beg Si Mor would not fall under the slow air category, although it is generally referred to as an air. Something like Valencia Harbour / Song of the books is a slow air, when played instrumentally.
Chris Langan, in the book “Move Your Fingers” is quoted as saying something along the lines of “The problem with young players today, and they didn’t have this problem before the gramophone and the radio, is that they hear good players playing difficult tunes well and want to play them right away, rather than learning easy tunes that will make them great players.”