Annoyingly, Amazon doesn't list how long each roll is. Presumably they're fairly short since it sounds like once you open the package you have to use the whole thing.
Digging some more, it looks like the 1" roll is maybe 40" long (the dimensions listed are weird, 40x1x2, I guess 40" long and the roll is 1"x2"?) which is not a huge amount but is probably about right for something you have to use up all at once.
The 2" wrap is apparently 50" long and the 4" wrap looks to be 60".
For $20 you're getting 12.5 feet of wrap. Not terrible, but it's pretty pricey if you want to play around with it and test it before using it on a real project. Still, if the product proves to be as water resistant and strong as they say, I could definitely see some uses for this.