This one was a big shocker, even among the NFL scouting community.
I don't know much about him, Bill Belichick obviously had his reasons for drafting him, so here's a few comments from NFL scouts when asked "who is Tavon Wilson?":
"Good question. Big surprise. Tweener type. Has been a cornerback and a safety so there's some position flexibility. Little rich for me (that high in the draft)."
"Our guys didn't have him graded high. They must have seen something specific they liked."
"Tough, physical run support safety. Liability in coverage."
Keep in mind that Patrick Chung will be a free agent after this season. He's more of a strong than a free, like Wilson apparently.
That's all I have for now.