Pros
SimulTrans has been around for decades. Similarly, most of the managers have been at SimulTrans for over ten years. Therefore, unlike most localization companies, it had a strong record of stability, that can be gained only through loyal customers and happy employees.
I learned so much at SimulTrans! My manager was extremely knowledgeable, and I really felt supported by her and the project and process management tools (based on Lotus Notes, that that company has developed internally and refined over the years, allowing immediate access to project costs, vendors, etc.).
No other localization company has such a significant impact on Silicon Valley's localization market, in terms of teaching localization to many people who now lead client-side localization programs throughout the Valley. Silicon Valley is certainly a better place, thanks to SimulTrans.
I especially enjoyed my interaction with colleagues in other offices, such as Boston and Dublin, that SimulTrans established long ago.
It's an extremely cohesive and supportive company.
P.S. As a parent, I was especially thankful for the company's accepting my need to be with my kids, leave the office early, work at home when they were sick, etc.
Cons
Some of the sales people are recent college graduates and lack the maturity and skill to stick with it (common problem with millennials' generation). I have heard that more experienced account managers have been hired.