1. Mensah rushed for 132 yards on 60 carries last season with 1 TD. The 5 rushes per game suggests that he has some mobility and the threat of him running is part of the game plan. That said, just 2.2 yards per rush, 1TD, and his longest run of the year was just 22 yards suggesting he is not a true "dual threat" QB. I'd say the answer on "mobility" as the NFL needs it is probably a mild yes.
2. This is a big question mark for him. Mensah had a hugely impressive yards per pass number of 9.5 but the folks who have scouted him say his short and mid-range balls are far more effective than his deep throws. He's got a good arm -- no way to get a 66% completion rate without the ability to zip it into tight holes -- but does not as yet possess the kind of elite arm strength that NFL scouts really want to see.
3. Mensah is listed at 6-3, 200... that is right at the average size for a NFL QB. It is generally accepted that if you are less than 6-2, you could have issues seeing over the line so guys who are shorter than that need to have some other aspects of their game to make up for the height. That said, there are not that many NFL QBs who stand more than about 6-4.
According to this article:
Bottom line is that Mensah has several of the attributes that one might desire in a NFL QB... but is far from being sure-fire prospect. In terms of physical tools, he is at least partly there. It seems grossly obvious to say it, but his pro future will likely be judged based on how he performs next year at Duke against power conference competition.