Well if it's the only offer, then take it. Working for a bank is better than working at the local pizza joint for a summer job. The money is a lot better. The unique experience you'll get at a bank is the auditing (in the code sense) and all the regulations you'll navigate.

Bank programs have to run right all the time. On a game like Candy Crush, a bug might crash someone's phone. In a banking application a bug might lose someone a lot of money. The bank dev process may seem slow to how you crank things out in school, but it's like that for a reason. Ensuring correctness and complying with all the banking rules are paramount, and will probably benefit you a college student.