I'll warn you, bivy bags really suck.

Source: I've spent in total something like three weeks camping in them, including many days in horrible rain.

Moisture always collects on the inside of them to a degree, because your body perspires, and the bivy bag interior is colder than you are. I have a really fancy and expensive gore-tex like one, and even it still gets a bit wet in the inside.

They're also really claustrophobic during wet weather when you have no choice but to lie down and wait.

These days you can get ultralite tents that weigh about as much as a bivy bag, and pack down almost as small. I strongly recommend getting one of those instead for places like the Netherlands where extreme winds aren't a concern.

The only reason I personally have used bivy bags is 1) desperate trips where I really needed to cut down on weight and bulk, or 2) because I couldn't bring a tent, and wanted to buy something cheap and lite that I would throw away later, or 3) intentional camping in places like caves where you are already protected from most weather and just need to keep drips off.

Now, all that said, the Observer bag you got it kinda tent like... and it weighs even more than my lightest tent!