I have decades of foraging experience, have many books, confer w/many foragers (including those who sell to restaurants) on Yahoo! Groups, and I can say definitively that if it looks like an onion, and tastes like an onion, then it is an Allium species. All Allium species are edible, period. Though, like w/anything, there are limits (even too much water isn't safe, in part due to electrolyte imbalance...), and like some foods, cooking can dissipate the strength (try eating a bunch of raw garlic cloves and see how your stomach feels, or try mild roasted garlic and watch how many more you can eat w/o stomach issues...).
Sam Schaperow, M.S.
Forager