Henrik,
As far as conventional double rifles go (sxs):
The Krieghoff is adjustable in it's horizontal plane but not vertically and only up to 375 H&H. The Blazer S2 is adjustable but I'm not sure in which directions. There are other guns around that are adjustable, the Valmet and Tikka. The adjustments are generally simple and not a complicated devise by any means. I can't imagine any reason it won't hold up over time.