Android App beta testing with TestFairy

I am thinking of trying out TestFairy to have my latest Android app beta tested. If their documentation is to be believed the processs is very simple and offers a great deal by way of contol and feedback.

However, I have one niggling question - one which their support have refused to answer which in my book raises a red flag even before I start. The question quite simply is this - if one of my beta testers clicks on the TestFairy URL they get will their Android device flag up an alert about how App installs from "unknown sources" is blocked or does TestFairy get treated as a trusted source by Android?

It seems strange that they do not make this clear in their docs and cannot be bothered answering when I ask the question of their support team. I am hoping that someone here will have the definitive answer.