Vantaggi
Red Hat is great place to work, if you're someone who likes to push themselves forward, create your on thing and make your own calculated risks. The company has a great future, built on solid re-occurring revenue model and is not dependent on any VC funding rounds. This model allows them to hire thousands of software engineers who work on upstream open source projects.
Svantaggi
For me, very little. Most of the reviews on here that mark working for red hat as unsatisfactory, are likely to be sales / services personal, who find it hard to adjust to the culture (having had former careers at IBM, Oracle etc). I have also heard the middleware consultants tend to get burned out quickly. Red Hat is very much an Engineers company at heart.