Are you folks (with keys) using the C natural key to sharpen the C sharp?
In the second octave, yes. In the first octave, usually not, although I’ll sometimes do so on a sustained C#.
Yes, the C sharp is especially flat in the second octave.
I automatically use the thumb hole on both C sharps on flutes with the
C natural thumb hole. The first octave C sharp is less flat on
the Olwell keyed flute, and less improved by using the key,
but somewhat.
Wondering whether to train myself. Thanks.
sure
you mean ‘house train,’ don’t you.
bit late for that, innit?
I was replying to the OP…
I hadn’t noticed that ya got in a response to Tintin 
I tend to vent most everything if I’m goin’ slow enough
See my reply in the other thread. And play 2nd 8ve C# “correctly” oxx xoo, - on pitch (usually) and more convenient.
Thanks for the info. needing to minimize use of L1
For me, in the first octave it considerably changes the tone of the note.
Feels like the note loses some of it’s overtones and sounds too sharp in the tunes (used to hearing whistles, keyless flutes, pipes play a somewhat flat note).
Been playing some Québécois tunes in A. In those tunes it seems more than appropriate to use the C key to raise the pitch.
I’d try to use the key in the second octave on any melody notes if/when they come up.
My flute is a Clinton Equisonant with brille, so the flute does that job for me!