I hope that the problem Ten Hag had in United wouldn't affect him again. Whereby, he buys young players who cannot meet up with the tasks expected from them by the club. Ten Hag might not be able to transform United, that doesn't mean that he wouldn't do well in Leverkusen since much pressure wouldn't be on him. He shouldn't disappoint Leverkusen and make them feel that they made the wrong choice to hire him to manage the team.
Manchester United and Leverkusen are not the same. The two clubs have different scenarios and different goals. At Leverkusen, ten Hag will not have the big funds to buy players. So ten Hag will have to try to find talented players. On the other hand, Manchester United had a lot of star players. Managing so many star players was also difficult for ten Hag. Ten Hag will not face this kind of problem at Leverkusen. My guess is that Leverkusen will not fight for the title next season. They will try to keep their performance stable and secure a ticket to the Champions League.