I LOVE the convenience of the these bags and I'm very interested, but what prevents me from pulling the trigger is the fact that they don't get returned when I send them in. I'd even be willing to pay very small fee (probably no more than $5 total) to have them shipped back with my books. Otherwise, the value is greatly diminished. I have so many bags and boards, I can make my own window bags at very little cost other than time and effort.
If anything, I'd probably get a pack of these for when I go to cons (when they come back!!!!)