Jef, Thanks. I did overlook the obvious source of this info! mike - - - -thanks too, Bill! 
I bought a small Pignose amp recently, and am perfectly pleased with it. It is probably true that the distortion is a product of passive pickups on the instrument and a maxed-out volume knob on the Pig.
However, I think you’re right. Whether or not you use amplification depends largely on who else is playing. For example, if you’re the lone whistler in a session with 3 squeezeboxes, 2 tenor banjos and a Hardanger fiddle, go ahead and use the Pig on your whistle. If you’re playing with a guitarist, you may want to go unplugged and let the guitarist plug into the Pig.