It's better to play regularly in a club that is fighting to stay in the Premier League than sitting on a stronger one's bench, isn't it? Also, Southampton's squad is very strong without Shaw and Lallana(and I understand that Lovren and Schneiderlin could be gone too). They got a lot of money to buy new players, and Koeman is a great coach. We'll see. I hope they will find a good place for Atsu, it shouldn't be that hard if "half the PL and the Bundesliga" want him.