Nostr is a public protocol, and all public data is freely accessible to anyone. You don't need a client to access it. Nostrich doesn't even operate a relay, which stores far more data than a client that simply serves as an interface to the protocol.

As for the source code, we've released it under the MIT license on GitHub. The code currently available powers all our applications, including Nostrich mobile apps and Nostrich Deck, since they're all built on the same web application and packaged using WebView. There are no separate native codebases. The only native components in our mobile apps are the bottom navigation and app menus, which we implemented natively for better performance and a smoother user experience.

It's entirely up to users whether to use our apps. There are plenty of alternatives, and that's the beauty and freedom that come with Nostr.