Managers are paid to take decisions regards bringing in players. In cases where they have worked with certain players in the past, they are in the best position to judge whether :
(a) a player will play to his capabilities, put in a decent shift, both on and off the field...
{b} fit in and get on well with his team-mates.
The whole history of the game is littered with instances where a player, or players, just cannot perform under certain styles of management, but give them a move, and the transformation can be dramatic.
Hopefully dramatic transformations will be the the order of the day with the new TB signings! Time will tell...