Pros
I've been at this company for a sort time and sure there has been some changes that did not agree with people. That is expected. I came in after some of the typical start-up to grown up company change I believe. In my short time here, I have worked with many different teams to get the company ready for the big league. I have yet to find anyone that is not there to help one another out and get things done. Support from the top down seems very strong - I know I can count on my manager to provide the proper guidance as well as let me do my job that I was hired to do. I've been at a few startups and this one by far is the most unified in their objectives and from the top down supportive of that. C-level management down support means so much and it shows.
Cons
There is a lot of change going on, new systems, people, and shift in culture. All the natural part of change - this change is on the correct path. As expected, not everyone is able to cope with rapid change or the disorder before any company can bring order. Thus, this con is really not a con but could be for people that need well defined structure.