MaterialUI? Is it shit?

A brand new code base. Old codebase (old employees) used MaterialUI, locking in a lot of the styling and layout in their grids.

I'm trying to identify the pros/cons that can come from experience using the framework.

Some questions to spark discussion:

Anyone used this in production for a period of time?

Did it hold up? Did the designers hate it?

How was mixing this with SASS etc.

Cheers