Is it safe? Yes. It is the same savah.us site you use in the browser, wrapped in an app. No ads, no extra permissions.
How do I buy? Just like on the web: add to cart, pay with PayPal or card.
Does it work offline? The app keeps the pages you visited in your phone cache to load faster and works partially without a connection.
Does it update by itself? Yes, it always shows the latest version of the site. The cache refreshes automatically every day.