You are right about the tackling. Of the guys I have watched so far, he has been the best. Besides the cutups on breakdown, I watched the Oklahoma, Iowa State, and the Texas Tech game. I watched the Ole Miss game live and I didn't have any huge issues in that game with him except his struggles against the bigger receivers. His coverage was good in that game, he just could not get around guys to make plays.
I couldn't find the right wording for the actual report, but I wrote down I really like everything he does from the line of scrimmage until 10 yards out. Footwork, movement, hips, change of direction, and his ability and willingness to come up and tackle all got plus marks from me.
Something seemed to happen after that though, he was close to receivers but they still made plays, he lunged at guys as they made cuts and for a guy with that speed to end up chasing as much as he did bothered me.
I think in Nickel he could be very good, he has the movement skills to stick with quicker guys. I agree on your comment about his size and playing in cover 3.
I think he will do well at the Senior Bowl in one on ones and I think he will test well at the Combine which could move him up and if he is drafted end of day 2 I wouldn't be surprised because of the position, but I just can't give him a Day 2 grade.
We do typically see guys in the same light, so a little disagreement makes it more fun.