Don't think this is going to be usefull when your phone is stolen.
If the thief turns off the phone and does a reset, your phone is gone.
Although this might be very usefull if you lost your phone somewhere.
Also, what about the privacy? (not that there's much left of privacy anyway)
Good question. Cerberus has an option to prevent a thief from resetting your phone. At the minimum, you can configure it to wipe the smartphone if the thief tries to access your personal data. That's not bad.
Also it works if you lost your phone, like you said.
Privacy about what? And to who? (privacy is gone anyway :P)