I've got one, used it since day one.
btw, there was a thread on this previously
clicky
If you go check the old thread there is mention of a spoiler, I was thinking of getting one of those instead of the laminar lip.
As far as your questions:
how tall are you?
-- 6'
When you ride at 70-80 mph where does the airflow go? Up over the helmet or right at the helmet?
-- It hits the top of the helmet, the way I've been running it with the lip it breaks the airflow some.
Is it quiet to ride with it in any or all positions?
I'm looking for quiet most of all.
-- if you're looking for that magic pocket of air?? Me to, haven't got it yet.
-- but I do prefer this setup over the National Cycle wind screen
Tom Barber (the "Barbarian") has one of these and thinks it is the best windscreen he has ever used.
But he isn't as tall as I am.
-bvw.