Few service rifles have the fine machine work to be found on a K31. I have several pre WWII Mausers, which are equivalent. Commie Yugo mausers, though functional, are rough. (Original M1924 Yugos are very well made, Commie rifles are rough)
Few off the shelf service rifles are as accurate as these K31’s. They are not target rifles. But they shoot well. Every Yugo Mauser I owned required bedding and trigger work. My K31’s, one needed a taller front sight. Other than that, they were ready to go.
I remember paying $350.00 for a K31, and was glad to pay it. K31’s were rare, and they are starting to dry up. I predict prices will continue to rise. No one is ever going to produce these rifles again, the action is just too complicated and expensive to make.
The Mauser 98 action is a superior design. The Schmidt Rubin is an interesting design, and one that only the Swiss would put the time and effort making.
A straight pull action is fun to play with. I am not convinced it is the best for a military action, but for non military use, it works fine.
I consider the 7.5 Swiss as an outstanding design, it was one of the earliest smokeless jacketed rounds. I shoot 174 grain bullets at 2550 fps in mine, that is as good as a 308. No animal is going to tell the difference.
The 8mm Mauser is an excellent cartridge, kicks hard in a steel buttplated rifle
If you just want a rifle that goes bang, either rifle is fine.