I really don't pay much attention to mock drafts. They tend to be simplistic in their analysis of the Pats' positional needs. "The Pats desperately need a premier pass-rusher!" They often focus on a player that the Pats have lost, or are likely to lose, in free agency and instantly mock a player at that same postion a going to the Pats early.
First, the Pats' coverage schemes appear to be placing more emphasis on the safeties in the default 5 DB alignment. It was taken to an extreme in 2017 due to the loack of healthy, quality bodies at LB, but it was evident even in 2016.
From that perspective, the Pats curently have one excellent, relatively young CB, and two who seem pretty good who are both even younger (plus a guy coming back from IR, PLUS a potentially re-signable UFA special teamer who played well in 2017 as an emergeny starter for three games). Meanwhile, the Pats two long-time mainstay, template safeties both turn 31 in 2018 Camp. They have a third who's pretty good and relatively young, and, as far as we know, no one else who should see the field except perhaps on ST.
Since draft class quality depth at CB is virtually always much deeper than at safety, I'd guess that, if BB is going to draft a DB at all at #31 or #43, is more likely to be another safety than CB, though perhaps followed up with a CB in the 3rd or 4th rounds. Of course, this doesn't preclude the possible selection of a CB (or even an "LB-lite") who's had fairly extensive college experience playing a safety-ish role. The role in the scheme, and a specific prospect's potential to fit the role, are more important than the positional designation.
Then, too, the Pats have gotten by fairly well in recent years with a succession of UDFAs in a critical CB role - Arrington -> Butler -> Jon Jones (?).
Anyway, as always, we need to see what roles/holes are filled in FA first.
BTW - my latest wild-*** predictions are that the Pats re-sign Jonathan Casillas to help cover a lack of capable bodies at LB, and sign Frank Gore at vet-minimum for insurance at RB.