What I have always wanted to know was when does this oxygen absorption occur? In my experience the package never come vacuum sealed, and I have never vacuumed sealed package after using a few for bottling. Does this mean that the caps are compromised? It all seems a little vague to me.
That's what I've been curious about as well. Exactly how much oxygen can these things absorb before they're bad? Seems like all the time sitting in unsealed containers is just wasting their ability.
Anyway, I guess the only real way to tell if they do any good is for someone to brew a batch of beer and bottle half with regular caps and half with oxy caps, and do a side-by-side test at various intervals and see if there's any noticeable difference.