It's like Cerwyn said: Sport-Systeme Dittrich is a german manufacturer of real-steel guns who specialized in new guns that fire live ammo, but that look like historic ones.
You can find their homepage
hereIt's not the one you linked there, Sommarkatze, that's a far cheaper model... don't know that replica and the site says nothing about the materials used, but it has very good reviews there. The correct link from Zib-Militaria would be
this (the shop is very recommendable by the way)
Sport-Systeme Dittrich produce everything themselves, even the tools they need to produce the guns are produced by themselves
Being produced as real-steels, the guns are of superhigh quality, this of course is reflected in the price range. They have some extremely interesting guns for high-end WW2 reenactors or collectors!
As a german manufacturer they produce semi-auto guns only and you're right, Cerwyn, they also build their live-ammo models as pure decoration guns which do nothing but cycle dummy rounds manually.
The price list for their "modelguns" can be found
here. I am pretty sure, that these guns are worth the money, the prices still bring a tiny tear to my eye
I have never had a Dittrich gun in my hands but I own a Shoei MP44 (it's the airsoft version though).
Shoei has achieved a look and feel, that comes extremely close to real steel, but they're handicapped by japanese law: They cannot build their guns with steel receivers.
Don't get me wrong, the metal they use is of highest quality, it's sturdy, has the correct weight and even seems to age similar to the real counterpart.
But if you want to go the whole 9 yards, you'd have to go with the stamped steel receiver of Dittrich's MP44. Oh, but before, you'd have to decide if this is worth the extra charge of over £1.000 for you... or over £2.000 extra charge for an MKb42... or over £5.000 (!!!) extra charge for an FG42
Whole 9 yards always have their price
For me, it'd be Shoei all the way, but everyone has to decide that for him/herself
If you guys want to know more about anything on the Dittrich homepage just let me know, I can translate for you.