(This questions asks for an opinion which, in most stackexchange.com forums, is discouraged. I'll answer, but would appreciate knowing what is allowed in the robotics.stackexchange.com forum.)
The major difference between most Linux distributions and Android is that features normally relegated to different users are relegated to different applications on an Android device. That is to say, all the Linux security efforts for isolating one user from another built up over the past several decades has been re-purposes to isolate one application from another. In this way, an Android device can safely run multiple applications fairly independent of one another. For example, your web browser should not be able to affect nor read the application you use for banking.
Is this good for controlling robots?
If you plan on controlling your robot from 1 application I would say it does not make any difference. But, if you plan on controlling your robot from multiple applications, using an Android OS would make it more difficult. Why? If you use an application for computer vision and another for mapping and yet another for motor control - how will they freely talk with one another? Likely it is not impossible. But such communication between programs is common place in most Linux distributions.