The "Most Expensive - Encryptor" app for Android is a tool that allows the user to encrypt and decrypt .txt files with a selected key file. The user can select two files, the first is the text file he wants to encrypt or decrypt, and the second is the key file to be used for the encryption or decryption process.

The application uses the Storage Access Framework (SAF) to access files, so the user can select files from different directories or external storage. However, before using the application, the user must grant the application SAF permission.

The application interface consists of four buttons: "Select file 1", "Select file 2", "Encrypt" and "Decrypt". The "Choose File 1" button opens a file picker to select a text file, and the "Choose File 2" button opens a file picker to select a key file. The "Encrypt" and "Decrypt" buttons encrypt and decrypt the selected files, respectively.

The app also includes a "Request SAF Permission" button that prompts the user to grant permission to access device storage using SAF.

The app also includes a "Help" button for detailed usage information.

The application uses a timer to show the user the time it takes to encrypt or decrypt a file. The status textual representation shows the progress of the message operation.