The test-tube shaped stage is a 'preform'. The shape might not be a huge problem, but it might not be trivial either. To blow the preform into the bottle's fi

The test-tube shaped stage is a 'preform'. The shape might not be a huge problem, but it might not be trivial either. To blow the preform into the bottle's final shape, it is reheated, and then air is forced into the preform, causing it to expand to fill the mold containing it. The issue you would see with a bottle like this is that when the preform is reheated, the plastic in the wall tends to flow depending on the final shape. When you have sharp corners, like those displayed, it is difficult to maintain an even wall thickness on the final bottle. So you either have to use more plastic than you want to ensure a minimum wall thickness is kept, or risk having thin spots, which hurts the structural integrity of the bottle. There is a reason that you don't see many square bottles. The ones you do see, like Fiji, are really thick to account for this. You can get away with thick bottles when you are charging $4 for a bottle of water. Less so when charging a quarter that price for soda.