The CHECK6 "feature" is IMO the most worthless idea in AH as it promotes people to get lazy and blame others for their failures. I don't give check 6's using that feature (if I do I'll use the text radio), and I don't want them to the point where I long ago deleted the .wav for it.
Far from saving me, they're just an annoyance. I haven't been shot down by an unseen plane since January I think. 90% of the CHECK6's I get (still seem it in the text, even with no sound) are when the enemy is 3K away in front of me.
I guess, in response to DejaVu, I don't view them as a courtesy, but as an annoyance.
J_A_B