I couldn't swear they work, but I'm willing to pay more for them for beers that are going to be aged a long time. Couldn't hurt.
Ditto here. I've used them for years.
Where I buy them, they are only $1 more per bag
. All I can say is that last year I opened a bottle of Wee Heavy that I made in the early 1990's, and there was no hint of oxidation in the palate (or if there was, it was certainly below my taste threshold as well as the two people I shared the brew with).
For the extra buck, to me it's a no-brainer.