The size varies, but the average weight is two pounds (about 1 kg.) It has a clean, crisp taste like button mushrooms. It is best cooked at least a little to develop its flavour.
These mushrooms are still harvested from the wild, though a company in Korea succeeded in 2002 in developing a way to cultivate them on a sawdust mixture. It is highly regarded in Asian cooking, and much in demand in Japan. It also grows in North America and in Europe, and is a specialty of Sardinia, Italy.
Disregard everything you have read about never soaking mushrooms. You need to soak this one first in cold water with salt in it, to coax out any insects camped in the ruffles.