Couple of comments....
1. Love the move of bringing Campbell back.
2. It add more depth to the DL and improves the position tremendously. He played 58% of the snaps last season. If that can be brought down to the 45-50% range, I'm certain he'll be an asset even at 39 YO.
3. It removes the pressure of being forced to draft DT in the first 2 rounds. I still expect DT in one of the first 3 rounds, but if the right player is there at another position, Monti is not forced to draft by need.
4. CC ranked 6th among DTs last season per pff. Getting him on a 1-year deal even at his age is a much smarter move than paying huge money for below average younger players. (See Kinlaw ranked #91 getting 30M garanteed)