Because SuitePOS is published on the Apple Store (unlisted and via enterprise distribution) it has had to meet Apple's stringent security requirements. In addition, it has had to pass Salesforce's Security review to be listed on the App exchange and has undergone certification via the various processing platforms we use.
The App encrypts any sensitive data (such as API keys) in to the Apple Key Chain and no credit card information is stored or exposed. All authentication to the underlaying platform (NetSuite or Salesforce) is performed using the inherent security models provided. These world-class platforms have world-class security.