Introducing Cover 13 years ago
Actually, their F.A.Q.[1] says that they do support this feature:
Is Cover compatible with a security code? (passcode, pattern, etc.)?
Yes. Cover is compatible with both PIN codes and security patterns. When you have a security code set, Cover’s “peek” feature is disabled. The app icons will slide across the screen, the security code screen will appear, and then the app will launch. In order to use peek, we recommend that you configure your security code not to take effect immediately. For example, if you set it to a 1-minute or 5-minute timeout, you’ll be able to use peek without sacrificing much security.