The Acme 560 is exactly what I expected. Compared to the Acme 660, the 560 is slightly bigger, slightly louder, slighter lower pitch, and about as easy to blow.

By the way, I can make a moderately loud sound with the following whistles by normally breathing into them:

Acme 660
Acme 560
Victorinox Distress (aka, TOPS)
Jetscream (but sounds like a lot of wasted air exits)

I have to apply a more forceful breath in order to can make a moderately loud sound with the following whistles:

Storm
Acme 60.5
Acme 636
Fox 40 Sharx
Fox 40 Sonik Blast