When I first try out a new flute I can usually quickly tell whether I gel with the basic sound quality of the flute. If it is a sound that I like, I will find what I call the 'sweet spot', the particular tone colour that I find easiest to produce on that flute - and I will revel in using that particular tone colour. I get carried away with the 'newness' of the instrument and simply expect it to do 'hard things' easily - crisp tonguing, low notes, high notes quietly - and because I expect it to, it fairly often does.
I come back to it later and play it again. I enjoy the 'sweet spot' of the sound, but don't revel in it quite so much this time because it isn't new to me. I start to notice other elements in the sound of the instrument and try to bring out these different sounds - can I push for more lower harmonics in the sound to get a 'darker' sound? can I make the sound really gentle and clear but without an 'edginess'? I get more picky, and of course, the flute - and MY technique - doesn't always satisfy my expectations. I lose abit of my 'revelry' and then the basic things eg. articulation, even sound throughout the registers - start to seem more of a labour again.
For me, this happens on ALL flutes. Just like it can happen in all human relationships!
I feel very happy with my Altus as I know that it contains all the possibilities in colour and expression that I want it to. It is my responsibility to keep my technique secure and (for me, this is my latest key revelation) - to keep my REVELRY - and then all is possible.