Pros
I've had the pleasure of working at Guardant Health for several months and there are many pros. Firstly, the people at Guardant Health are very positive and are truly interested in solving problems and saving lives. Additionally, the office has a very nice setup with a great kitchen, lunch meals, nice meeting rooms, and an overall elegant, modern design. Guardant Health is promoting good cultural values including humility and a desire to try new things. This really minimizes any kind of politics. Finally, Guardant Health is growing really fast and the future seems really bright.
Cons
There are probably only 2 cons, and they are minor. Firstly, the hours can be long. However, for a silicon valley startup, they are perfectly reasonable, and I've seen worse. Secondly, even though the office has a great setup, the open space can sometimes make it hard to concentrate. This can easily be mitigated by picking up your laptop, and booking one of the many meeting rooms.