IMO, not playable. The top 10 ranking is probably based on last year's defense which didn't allow many points and was an okay fantasy defense, but as David said it was mostly "smoke and mirrors" and they will almost definitely be a worse fantasy defense this year...David is NE defense playable this year? Most sites have them ranked in the top 10. Average is 9 or 10. How is this possible with the young defensive players they have? Is it because the NE offense will put pressure on the other team's offense?
Depends on the format; is there negative point potential for points given up? If so, run away, run away. However, if there is no negative penalty for points allowed AND STs are included then they are draftable imho.