The main part of the application is (and will ever be) freely available. The source code is open source and can be viewed and edited on Github.
However, there is a Premium version available, which currently adds two features:
- Remove all advertisements.
- Add the ability to configure more than one connection
- Unlock voice commands using Google Now
The Premium version can be obtained from within the application. On the top right side, there is a context menu including a button for the Premium version. Billing is handled by Google. There is currently no chance to bypass the billing service and buy the version using i.e. Paypal or other services.
The purchase will be associated with your Google account. When using a new device, just make sure to use the same account again. Google will unlock the Premium app automatically.
However, there is one pitfall when installing the Premium app a second time: There are two ways to obtain the premium version - from within the app and as separate Premium app. Please make sure that when you install the app you use the same approach again. When having purchased the Premium version from within the app, install the free app again. Google will take care of unlocking the Premium features again. When having purchased the Premium app directly, just install the Premium version again.