To wit, I've encountered them for years and I still have no idea what a floating circle with a plus sign in it is supposed to represent. Almost every time I've clicked one, it's begun a process of flow that was not my intention, so I've learned to avoid them.
What Material Design is trying to do is to create a universal design language, based on the assumption that different apps designed in all sorts of different ways is a bad thing. While I admit that bad design comes in many shapes and forms, I actually feel like the context of an app should dictate how it is designed, and that in many cases it will call for something other than bold colored boxy components with assorted degrees of box-shadow.
For example the text input box not having borders and all the slow animations. I struggle to think of a situation where Material is better than just basic css.