As you say, could be a good addition. His age is important in this as he's only 22 and been playing 1st team football, I think the policy moving forward will be to buy young players and improve them. I fully expect to see Bissouma in the team more next season.
This guy looks like he's got all...
From wiki if anyone was wondering about the cucumber reference:
Full name
Club Deportivo Leganés, S.A.D
Nickname(s)
Los Pepineros (The Cucumber Growers)
Lega