it takes guts to eat that stuff i'll say! i don't have any digestive problems normally, but wasabi puts a fire in my belly that lasts for hours and as for your friends, you should blind fold them and have them eat some it's delicious! when i had some last it was on a bed of what i think was pickled cabbage (omg...it was amazing)
So tempting! Well, I suppose a huge amount of wasabi isn't needed when it comes to wasabi. I like the spice. My stomach can handle sooooo much of fire, but it's considered to be poor taste to use too much for Japanese food anyway. I like the ingredients to speak for themselves.