Foil bags with check valve for storing hops?

I came across this BYO Mr. Wizard article on storing hops:
http://byo.com/mrwizard/923.html
He mentions that you can get zip-lock foil bags with a check valve from coffee places that are great for hops - put them in, seal, and squeeze out the air. That sounds great, so I searched the web a bit and found some places selling them. For instance, on ebay:
http://cgi.ebay.com/60-One-Way-Valv...Z005QQcategoryZ146218QQtcZphotoQQcmdZViewItem

Has anyone used these? In particular, do the check valves really seal well, or will they leak some air back in if you try to squeeze out every last bit of air from the bag? The price isn't too bad in the end, but to be economical it seems I need to buy a lot of them at once, so it's not so cheap to just test them out to see if the valves are good enough. I'm looking at buying some bulk leaf hops soon and this seems like a good storage solution, a pretty big step up from ziplock baggies.

I've never used them or even heard of them for that matter. I vacuum seal large quantities of pellet hops, but also have smaller quantities in standard ziploc baggies in my deep freeze and have yet to have any issues.