vicenzo3006,
Here's a discussion of this particular sling as it relates to authentic German WWII slings.
http://www.bergflak.com/slings2.html
Noted authority Claus Espeholt, on the other hand, seems to believe that the Germans did indeed have a sling made to this pattern late in WWII. They were completely unmarked, however, and had construction and retaining buttons that differ from the one you have pictured. The button was made of zinc and each side of it was convex (not flat) and identical.
http://claus.espeholt.dk/slings.html
I have two of the unmarked slings and believe them both to be authentic German WWII. I didn't pay much more for them than a few bucks, though, and wouldn't until the authenticity question has been resoved with original German records, including drawings and production records, which so far have not surfaced.