Pros
The people I worked with while at Lab are among the best engineers I've worked with. Not only did I learn a great deal from them, the relationships I built while at Lab continue to be important to me. Lab projects were also generally interesting and short enough that if they weren't, it didn't matter that much.
Cons
Lab is a consultancy and suffers from the usual consultancy issues. There's a lot of turnover in the workforce, and projects can be highly variable. The particular projects you land on can have a lot more impact on your experience than anything else. The ION acquisition was also highly disruptive to the historical Lab49 culture. Do your research, and read the news stories you can find on ION group acquisitions and the way they've been perceived by ION's employees, customers, and lenders.