Three main things here for me:
1) He would probably have been at least a squad player for a Championship side next year, so for him to have been impressed enough by OUFC to return here says a lot about what's going on behind the scenes at the club. I would imagine he's taken a bit of a pay cut, too.
2) Credit to KR and the board for getting business done early. MM hitting the ground running after a full pre-season with the club could see him in contention for POTY next year if we're still in League One.
3) Credit too to KR for obviously having learned from having his fingers burnt previously with regards to announcing this early. I doubt he'd have made the comments he did about MM a few weeks ago if the deal wasn't guaranteed.