This is a very nice and practical set, especially with its case!

Those combination sets (one barrel pair rifle/shotgun, another barrel pair shotgun only) were actually quite common. At first as side-by-side gun, then also as over-and-under. And you could have even more barrels

The most extensive combo was also made by Simson:
https://www.germanhuntingguns.com/bengt-bergs-fantastic-set-of-simson-guns/