I'm glad they're willing to keep their options open. But the thing about a 10-day contract is that the player has to get run to see if he's worth keeping. I feel like Wemby isn't going to sit unless he absolutely has to, because he wants DPOY badly. Kornet has been missing time recently, so maybe he'll sit. The only other option is that the Spurs might want to experiment with Wemby and two centers in the rotation.
There was a time when Mason was considered to be a decently skilled big (this is before Victor and the Jokic-archetype, obviously). He could put the ball on the floor and dish it. He's not a shooter, but he provides a different kind of vertical spacing than Kornet, as he doesn't need his guards to get him the ball all the way at the rim. He's probably not a rotation piece, but he could fill in.
Best thing about this contract is that it's over before the buyout deadline. The Spurs should be actively working with vets to see if anyone is interested in signing on. This isn't like normal free agency where that sort of thing is tampering. A lot of times, vets won't take a buyout unless they have their next team picked. So the Spurs can and should be courting options, even as they give Mason a chance to show what he can do.