We have added over 18,000 US banks and credit card companies to Level. These banks need to be tested before we can confirm that they work well with Level. They are fully secure, however they may not connect perfectly. In the event that this is the case with your bank, please drop support a line so we can identify any issues that occur.
You can connect Level with a new bank by opening the Menu > Settings > Connected Accounts, and then hitting the '+' icon.