Currently v0.0.2 has indeed a similar UX & feature set to sherpa, but already now you can highlight any text, click share, and then send the text to voca to start it reading. That's a big UX improvement already, and just the beginning. Soon you will be able to share pdfs, epubs or websites with voca to instantly start reading them. And eventually you can add text to a queue in voca to bookmark for later reading, kind of like a podcast app.

In short, Sherpa is primarily a text to speech engine, while voca is primarily a reader app.