Pros
F5 bases its success in team work, even with "competitor" companies. That is also reflected in the employee level. I have never had so much confidence on knowing that I can trust my teammates and other experienced people from other teams. You will always get help from others. F5 does amazing stuff that is "secretly" supporting things that millions of people worldwide use, from mobile carriers to banks, government agencies, etc. You feel the impact, the challenge and that helps you respond with commitment for excellence. Very competitive salary, great benefits that challenge the huge multi-nationals. Plus again, the culture is something that makes your day worth to be in the office, the atmosphere where everybody understands we are in the same ship and we need to sail it together.
Cons
The company is growing really fast and sometimes you get the feel the company is not ready for it. However it still feels like the start-up company which is learning and available to change in order to improve.