Guten Morgen!
A bit late to the party, sorry!
MFH is like Mil-Tec a German trade brand that offers very bad Asian made equipment in army stile.
The best military bivvy bag is the Carinthia Goretex sleeping bag cover with gas permeable technology called fabric.
Only this one currently allows you to breath through the fabric of the fully closed bag. Nevertheless you will get during 8 hours sleep a moisture problem inside, so you have to breath outside anyway. 900 g and very expensive with very well water protected central zipper.
This and the older version with the normal Goretex jacket fabric can be bought used from the German army, some older ones were made by Feuchter in Germany in best possible quality.
The entry to and exit from the British army bivvy bag that can be found even unissued for 10 % of the price of the current Carinthia bag is a bit acrobatic. No problem if you are 16, rather a problem if you are 60. Less good for hot climates because it has no zipper. Otherwise it's rain and idiot proof. 800g.
The right choice if you are young, strong and poor.
The lightweight option is the already above mentioned Sungpak Special Forces bivvy bag, 350 g only! Made in UK, not far east!
It costs the double of a British army bivvy bag unissued or the same as a used German army bivvy bag and is for civil use a very good recommendation.
Of course it doesn't last as long as a Carinthia bag but for the rather low price that's absolutely OK. That's also real military equipment with NATO Stock Number NSN.
I talk here about nothing else for good reasons, also below:
Men can pee out of a German army bivvy bag or Snugpak SF bivvy bag without leaving it. You simply roll onto the side, open the zipper and wee downhill. Very funny from the sofa. Good to know in reality out there. But an additional poncho, for example the very light Defcon 5 water poncho, 350g, that's also issued in the Italian army, that can be used as additional plough point or lean to shelter is good to have without any doubt, especially if it rains already in the evening.
I recommend to put the bivvy bag onto a closed cell foam mat. That's practical and protects the expensive bivvy bag.
For the Summer for example Multimat Adventure 4 XL, a copy of the German army folding mat, or if it's less warm the Multimat NATO mat, what's the issue British army roll mat, that also can be found used and cheap. The Adventure 4XL is issued to British parachutists.
The normal size of the Snugpak SF bivvy bag is smaller than the Carinthia bivvy bag or the issued British army bivvy bag.
All three are very well constructed and work technically very well. All three are worth the money if bought new or can be found used in very good condition.
The plain green British army bags are obviously over aged. My three ones lost their seam tape. The new MTP ones are obviously the better idea.
Decide what you like among these options and it won't be a fault in any case. It depends on your age, planed activities and pocket money.
I have all three options at home and it's also if already payed still a pretty difficult decision what to take. As you see, you can easily choose the cheapest option if you are able to enter your sleeping bag without opening the zipper.
Otherwise get one with a zipper!
Well, the German one is the best, but we talk about nuances here. The Snugpak bivvy has a draw string that's sometimes a bit in the way, but if you put it between bivvy and sleeping bag it's not such a problem. But well, the German one hasn't that draw string because it's a bit better constructed. It's roomier, what's mainly interesting if you want to take your boots into it below the freezing point. You can enter it more easy than the issued also roomy British one and can wee out of it like you can out of the Snugpak SF but not out of the issued British one. And the German ones have surely the best quality and longevity.
If you could get a used one that looks like new and costs only 50 € made by Feuchter in Germany you should take it of course. But if not, well get one of the both others. They are also really good!
The Snugpak SF is outstanding light.
The British one is idiot proof and I like that very much. A real no nonsense construction of the best! Perfect equipment for young men.
And I have to tell you, the older I get the more I hate unnecessarily complicated equipment.
And don't forget: If you burn a spark hole into a 50 or 100 € bag it's probably less shocking than discovering that at your factory new bought Carinthia Goretex sleeping bag cover for currently 515 €.
I mean the issued Brits in good shape you can get for 50 €, sometimes even new old stock, and if you are inside, it's round about the same!