Pros
One can leave very big impact because Palo Alto office is used for new project|products and they are mostly independent from HQ. So you have a feel of midsize company (think 50 engineers) but stability and perks of big company (~500 engineers). They like initiative and encourage engineers to think about big picture and come up with what to do. And the last point is cool cultural mix. The company was born in France but french are minority in this office so don't be afraid of being overwhelmed. As for work and life balance. I keep hearing that so much from my friends working in Sillicon Valley. I think Criteo is unique in SV. Work-life balance here is not something HR are trying to force for people not to burn out. It is natural here. Just look at amount of day offs and respected holidays.
Cons
There is 10 hours difference with HQ