Pros
a) Challenging environment: as a technologist, this is one of the most exciting places I have ever worked. The problems being addressed are big and solutions demanded are creative and exciting. b) Fantastic team mates and management: You are working with some of the brightest minds in the industry. It is not just that they are extremely smart but starting with the founders, they have a superbly positive attitude, demanding yet willing to listen. They are technologists and hence can understand your problems and work with you, not just manage by spreadsheets. c) It is fantastic to work in a company that has high visibility and seen as a shaker and mover in the industry.
Cons
SiFive competes with the Giants of the industry. The pressure never lets up because we are going against companies that are dominating in the field.