Download and try the app before you donate. Follow the instructions below for downloading apps from non-google play sites.
PayPal Simple Storefront
To get your phone ready to download an app from a non-google play site, follow these steps:
Tap the Home button to go to your phone's Home screen.
Tap the Menu button, then Settings, then Applications.
If your phone has an Unknown sources setting, make sure it is checked.
The most simple way to load the app is to navigate to this page with your phone/device and download to your phone. After downloading the app, it will prompt you to install it. Tap the "install" button.