Vantaggi
Their engineers are their assets and selling points, so the better you are at what you do and your reputation in the engineering community the easier it is for them to get new contracts and clients. Because of this they invest heavily into their engineers w/ books, con-ed funding and lots of tech seminars.
Even though it's a consulting gig they still some how make you feel like part of the Dev9 family. It was the first place where I started a new job and immediately felt like "these are my people". Medial benefits were amazingly affordable considering the size of the org, I was really impressed at that.
Svantaggi
Their office in Kirkland is old and smells funny, but they are moving in January 2016 and we spend most of our time at the client's offices so it really doesn't matter.