Pros
Model N's work has a clear purpose. My manager was flexible about my hours and vacation time. I did not encounter issues with office politics or favoritism. Model N is more willing than most employers to sponsor foreign workers who need H-1B visas or other sponsorship. (Perhaps as a result, the workforce is more diverse and international than in the average company, with a particular focus on workers from India, where Model N has an office.) The Redwood City offices are modern and clean, with good facilities and computers. The company is profitable.
Cons
My salary was lower than I would have received at other tech companies in the area. Benefits are just the basics, like health insurance (e.g. not like Google, with free meals, the ability to take your dog to work, etc.) Model N's financials were poorly documented in its early years, resulting in long and difficult audits. Management has been promising an IPO since at least 2006, but it never comes. (At one point, they almost had it, then called it off when the economy turned bad.) There have been large layoffs in the past, correlated with bad economic times (the tech bubble burst, etc.).