This was a concern for me as well. Brand new relationship with a company: now here's all my most precious banking credentials. There needs to be a lot more assurances around this.

In our case, I used bank creds, and immediately changed them to something else.

One other point of feedback. The AWS rewards is a big draw, but you learn new conditions only after you sign up. I don't think it was intentional but it felt a little bit like false advertising. Be sure to state all the conditions upfront that are required to win the rewards.