It's understandable why Kevin Spears was a 3star. He didn't show much quickness or break away speed and would also go down very easily.
Spears actually has pretty good speed but the thing I like on this video the most is how good he is catching the ball in traffic. About 60% of the video is him catching between 2 or 3 defenders. Leaping and catching ability are above average. He'll get stronger in the weight room.
The video was more or less showing you what is perceived to be a 3 star (me personally I think after a year of training he'll be one of our top receivers). Jalen Mills, Morris Claiborne, Tyrann Mathieu are 3 recent DBs that Miles has used the Third Eye on and has gotten tremendous results.