Vantaggi
Sirris is an unusual not-for-profit. Business is amazing, revenues are stable or growing, profit is never an issue. For juniors, work can be quite interesting thanks to the Belgian industry-wide helicopter view Sirris enjoys. Great for PhD students: salaries are higher than the scrawny grants Belgian universities pay. If your research topic is of interest to Sirris and you are currently in a Belgian uni, joining while pursuing your thesis is a very smart move. There is some job stability. Stay put for 2-3 years, always say "thank you" to managers. Also, factor in the 50% home-working time you get.
Svantaggi
Despite the internal talk, salaries are lower than in industry. Managers are mostly science PhD-like profiles who earnestly believe "management is easy". They promote people to their "liking", meaning that the best odds are with a) males b) Dutch-speaking c) who hold science PhDs. Look for people they "like", and notice there's a lot of upward politicking, cajoling, flattering. Downward, expect manipulation (pushing the right buttons) to keep subordinates in check. Everybody else: even if you are a top-star performer, to be recognized for your contribution, join another employer. Despite sitting on considerable cash reserves, Sirris did some abrupt layoffs in the past n years. It fired top-of-the-line money-making machines, because managers didn't like them. Job stability? Really?