They are great rifles, and while I wouldn't necessarily call the 7.5x55 "potent", it is a nice round. Certainly, if one were to hunt with it, you could easily dispatch most of the game on this continent, but I don't think it is as good a round overall as the .30-06 when looked at from the perspective of "potency".
Also, not Swedish. Swiss. Big difference, obviously. Branching off a bit, the Swedish Mausers are a delight. The K31 are pretty accurate rifles across the board, but the Swedish Mausers are better. It is not unheard of to get sub-MOA performance out of them. Plus, the 6.5x55 Swede round is a pretty good round.
Back to the K31, if your interested, buy it. Out of all my milsurps, it is my favorite to shoot, because that straight pull bolt is just fun to work with. They are more accurate than I can shoot, and I have made hits, from a rest, from surprisingly far distances (out to 500 yards). From more moderate distances, say 100-200 yards, I have shot real, real close to MOA with the GP-11 surplus ammo. I assure you, you will enjoy the rifle, depending on the price. I actually am not sure what a good price for them is anymore, but the last I looked, around $200.00 for a shooter was about right. Also, there are commercial loads available for them if you cannot find or run out of the GP11 ammo.
From a sportsmans perspective, you certainly could hunt with one. There are scope mounts available. I have never looked, but I am sure you can find sporterized examples of them. Personally, this is one milsurp rifle I do not like to see sporterized, particularly if it comes with the previous owners tag, as you indicate this one does. While all milsurps hold a certain amount of nostalgia and respect for the soldier that carried them for me, this is the one rifle where you can commonly find a name and unit. Some guys have actually found the previous owners and chatted with them.
In any event, unless it is priced over the moon, I heartily recommend the rifle.