At the moment we don’t support the ability to completely block the user from playing your game on a mobile device, we only support the compatibility warning.
It’s unlikely we’ll add an option to completely block it, the reason is that the power of mobile devices is always increasing and the line between mobile and computer is continually being blurred. For the sake of future players, giving them the option to run the game will ensure they will still be able to access the game whatever device they may be on.
Hope that explains