What a great idea this is! Being able to vacuum seal without the need of electricity would be a great thing to have...especially when there is no electricity! I love that you can reuse glass jars you already have...without having to purchase some special jar from the manufacturer. It can also be used with zipper locking bags.
Here is a great video demonstrating the pump-n-seal.
Here is the official instructional video.
Here is a comparison of various vacuum sealers. (Done by the manufacturers of pump-n-seal)
I'd recommend stocking up on a healthy supply of those little yellow "band-aids" if you buy one.
This is a great way to fight one of the main enemies of food preservation...air!