Regarding Android, it’s be great to have Android on Better. However, Google have officially banned ad blockers from Google Play (http://www.androidpolice.com/2016/03/01/google-explicitly-bans-ad-blockers-from-the-play-store-except-all-those-ad-blocking-web-browsers-apparently/). So the only way to make a tracker/web malware blocker for Android is to create your own browser—that’s a very different challenge.
As most people use the system browser or one of the other popular browsers on Android, and are tracked constantly and natively by Google on the platform, it would both be an uphill battle and offer a false sense of security.
Since we're just two people, we have to focus our energies on where they can have the most impact.
That said, the code is freely available and all of the blocking rules are available under Creative Commons ShareAlike, so anyone can port it to Android if they want to help with that
I hope this explains why we picked iOS for Better.