Since it's developed by Google (who are also responsible for the creation of the material design guidelines), it ensures a high level of quality and tools available.
Material Design can be recognized on products through different companies that used them. You can loose your identity.
Every Topcoat component is built with performance in mind. Most of the stylesheets are small and do not take too long to load.
For some components the text size is quite small, while for others it's too light over a light background, making the text harder to read.