He's been a manager in same league for past 4 seasons he knows the players inside out especially with Brentfords impressive data collection & database.I think Frank is the type that wants to see them in training before assessing them. I don't think he is the YouTube highlights assessing type.
He will likely need to see the kids in training and on tour but he should know day 1 whether likes of biss, bentancur, Johnson etc are players he can put into whatever system he wants to play