Lego's robotics stuff might be patented but their core brick isn't anymore. However the generic replacements like Mega Bloks just don't snap together nearly as

Lego's robotics stuff might be patented but their core brick isn't anymore. However the generic replacements like Mega Bloks just don't snap together nearly as well as LEGO. For a toddler making a little garden out of a few blocks it's fine, but you can easily make a vertical Duplo stack that's 3 times taller than the maximum stack you can make with Mega Bloks, and that kind of structural integrity becomes very important in robotics.