Shiny! Are those replaceable jaws?
No, it's a stop. The open end has 30° positions. In the 'normal' position, the open end behaves like any other open ended spanner, but if you rotate the tool through 30°, the stop will retain a head. This helps if you need to hold a nut in place with the spanner, to get it into an inaccessible location. They've put a lot of thought into these spanners, but consequently they're expensive.
I think this part has to be bolted on, because of the nature of its construction, and any spares do not appear to be easily available.
Wera Combination Spanner