Passenger side has a much larger airbag that helps prevent the head moving off to the side (think of hitting a pillow dead center, verses toward the edge). I wouldn't expect the Ineos dealer to know/care they are just selling parts.
Here is a video of a Toyota 4 Runner that illustrates how the head sort of 'grazes' off the side of the driver's airbag and heads toward the pillar.
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I hope no one ever has to find out, but odds are someone will. Its your family, and your decision, just wanted to make it know for you (or anyone else) that may not have thought about this reality before they decide to do the same..