Apps that support authentication
should work. That means the app needs to allow you to subscribe by entering the URL, and provide a way for you to input your GTD Connect user name and password. (Note: Your user name may not be the same as your email address. Email
connect@davidco.com and we'll clarify.)
I've just tested on the native iOS podcast app and Downcast, and they both work. On Android, I've both BeyondPod and Podcast Addict both worked just now.