All currently offered new Carinthia bivvy bags have the same Gas Permeable Goretex. Older ones had the usual jacket Goretex, approximately like Fesca and the British ones.
The Carinthia Tropen sleeping bag has a moskito net, the standard Carinthia (German army) Goretex Sleeping Bag Cover hasn't. It's unnecessary because you could close the bivvy totally in cold conditions when you tend to use the Defence 4 sleeping bag.
If you don't prefere the lighter and cheaper Snugpak Special Forces bivvy bag as I do, the Carinthia bivvy bag with central zipper is the way to go in my opinion for every civil use too.
The German army ordered this as the standard issued one because it's the best option for most users in most situations.
If you sleep in the open in the rain the Carinthia bivvy bag zipper flap forces you to sleep on your right side, the Snugpak Special Forces bivvy bag forces you to sleep on your left side. It's worth to think about this detail before you order one.
The Snugpak SF bivvy costs new as much as a used German army Carinthia bivvy bag , approximately 100 €.
If you want the Gas Permeable new fabric you need to pay attention, because the old ones with the jacket fabric looked the same! There must be written on the label inside "Gas Permeable Technology" or "Gas durchlässige Membrane".
I wouldn't buy used Fesca products. You can read everywhere that they have problems with broken zippers and the seams also aren't so accurate, what probably doesn't matter though.
But what matters is that you get condensation water problems in a hooped Dutch army bivvy bag if you breath into it. They issue additional a poncho as shelter for standard use.
The hooped Dutch army bivvy bag isn't meant as a stand alone solution for comfort camping. That's no double wall tent!
One could say, especially from the point of view of a civil user, that the hooped Dutch army bivvy bags are constructed wrong.
They surely work well as stand alone solution if you need four and a half hours sleep next to the enemy somewhere. That's what they are constructed for. If the soldier needs eight hours sleep, he has to construct additional a poncho shelter and doesn't use the poles.
In a Snugpak, German army or British army bivvy bag you can sleep as long as you want like a baby!
There are older green simle Dutch bivvy bags too, that allow you to sleep long. These are offered cheap and have a central opening that allows good ventilation if not closed totally, what's important if it gets hot and is more comfortable to enter than a British army bivvy bag. Important if you use the bivvy bag sometimes also in a tent. That is sensible to keep the sleeping bag dry and clean and adds a bit more warmth to the sleep system.
When I carry a tent I don't leave the bivvy bag at home and can choose to sleep either in only the bivvy bag or in bivvy bag and tent. I prefere to keep the options open.