I'm sure the canvas cutter has its place and I personally use bivy sacks quite a bit, but, as a stand alone shelter, you get in and/or out of that setup one time in the rain and you'll be looking for a new shelter. Bivy sacks are great for when there's no room for a tent, say, sleeping in a mule deer bed on a 30 degree slope, or for when there's little chance of weather and you want to be fast as possible getting to sleep and getting going. If there is going to be weather, you want a tarp overhead or everything inside the bivy gets wet as you get in and out and, getting dressed and undressed inside of it, while doable, absolutely sucks. That shelter is an option for someone with multiple shelters. Buying one as your only shelter without an overhead tarp (which defeats the purpose) is a big mistake.