Both the web version and apps have the same algorithm for writing style analysis and use the same database.
However, apps have the following additional features:
No limitation on the maximum text size. The web version is limited to about 30 kilobytes of text. The apps don’t have such limitation, you can process larger texts with them.
Top rankings and probabilities. In addition to showing you the most similar author, you can view the top three likely candidates and the probabilities of their style matching yours.
Offline analysis. This means that you don’t have to have an Internet connection to analyze your texts and you don’t have to send your writings to our server for processing.
Save texts and sync them across your devices with iCloud. The web version just processes your text and discards it.
Text statistics and readability. Apps show character, word, and sentence counts, and analyze your text for readability to show you the readability score and how long would it would take for an average reader to read your text.