I have on in my cart but I can't decide if I'll get it yet. Woot charges $5 shipping no matter the item, quantity or size. If you just get one MK5 it's gonna cost you $20, about what it would cost from Amazon (note: Amazon bought Woot a few years back). However if you order a couple, or anything else while you're at it, the shipping is distributed over more stuff. Right now they have some really superb Gigerrig hydration systems, for instance.
One thing I'll say is that if Woot is selling it then it's almost guaranteed to be legit, not a counterfeit. Can't always say that from every vendor.
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“I'd rather have questions that cannot be answered than answers that can't be questioned.” —Richard Feynman