I am considering this for a 5x12 balcony over a busy street. Both ends and the middle would be weighted with furniture. Is there any possibility of the tiles unlocking and flying into the street during high winds?

The possibility is extremely low since once interlocked, the weight of these tiles will keep them in place. If in doubt, you may use double-sided tape along the perimeter of the tiles to adhere them to the subfloor for extra safety.