He's definitely risky. But you have to separate out that he was the first pick in assessing how risky he is. Whomever the Browns had taken (Mayfield or Allen or anyone else), that player would represent so much draft capital that a bust would be costly. There's a certain amount of risk involved just in picking #1 that should be segregated from the risk inherent in the player himself.
If Nelson had been the pick he would have added very little risk to the risk of picking #1, since he is so unlikely to bust (though the cost of him busting -- i.e. the risk of picking #1 -- is the same).
Each of Mayfield and Allen have things to overcome. There are some off-field concerns with Mayfield, to go with his limitations in height. But we've seen other QBs (Brees, Wilson) overcome limitations in height and history offers several examples of QBs with 'off-field concerns' similar to Mayfield's that have succeeded (Namath, Stabler and, more recently, Cam). Aikman's point was that we haven't really seen QBs overcome Allen's limitation -- a lack of accuracy -- which makes him more likely to bust and therefore the riskier pick. I actually think when you factor in Mayfield's obvious competitiveness he's that much less likely to bust than Allen.
