The difference between the protective housing with the article number ADDIV-001 and the cheaper variant with the article number 50026631 could lie in the quality, material and additional functions. The protective housing with article number ADDIV-001 is specially designed for the GoPro Hero 9 to Hero 13 Black and may offer better protection and more compatibility with other accessories. The cheaper version might be less robust or have fewer functions. Unfortunately, I don't have any specific details on the cheaper version, so I recommend comparing the manufacturer's descriptions.