BuildInfo

You can obtain build version and number using the ISN_NSBundle class. It's much better to relay on this values vs unity Application.version - since it pretty much holds what you have set inside the Player Build Settings. And maybe not the same as real build version & number.

See the code snippet below:

SA.iOS.Foundation
...

ISN_NSBuildInfo buildInfo = ISN_NSBundle.BuildInfo;
Debug.Log("AppVersion: " + buildInfo.AppVersion);
Debug.Log("BuildNumber: " + buildInfo.BuildNumber);

App Environment

In case you need to know if your app was downloaded by a real user from App Store, or this version is used by a tester who got your app via Test Flight or in any other way you sent your app to him. You may check the App Environment.

This may be useful, for example, when you add to your testers some "extra gold" so it will be much easier for them to test your app. The code snippet below shows how to check the app environment:

if (ISN_NSBundle.IsRunningInAppStoreEnvironment) {
    Debug.Log("This app was downloaded from an AppStore");
}