Mane is a good player but I don't like his attitude. It's clear that this turning up late thing just at the start of the transfer window is a way of him agitating for a transfer.
When you are in tough times you need players who have the right attitude and commitment. Some players respect the game, respect their club, respect their team mates. Other players are basically individuals who are in it for themselves.
Tevez had an uneasy relationship with United and when he went to City his true colours came out. I would be wary of Mane.
I also think he is hit and miss as a player. He has occasional amazing games and then goes quiet.