Warning: new update has eliminated free premium UFO's. So if you have not updated to the new version. DON'T!!!
I have two devices(well, my iPhone and my wife's iPad, my wife is not a gamer at all). Fortunately I only updated to the new version on one device (level 22 on iPad, doesn't have a 5 star alien). The graphics are much better on iPad now. so I don't really regret updating it.
I still have the older version on my iPhone (level 26, has one 5 star alien). And I still can get free premium UFO's on my iPhone.
So if you add my main account 505071412 on my iPhone, I will send you a premium UFO from my secondary account (if you still have the older version).