Pros
This is a fantastic company to work for in terms of job satisfaction. In the two years I worked at FSI it was incredibly rate to have a day where I wasn't enjoying the work I was doing.
A large part of this was due to the people - I was incredibly lucky to have a wonderful team of co-workers. The development manager is absolutely fantastic and incredibly dedicated to looking after his team as well as helping them develop professionally.
The work itself was interesting and you really got a chance to get to know how the clients worked and how the product was being used. The good workflow management and process also made my life as a developer more straightforward than at any other company I've worked at.
The company's hiring approach is to recruit juniors with limited experience and then bring them up through the company - so I would highly recommend FSI as a good place to start your career. It's fairly small which means it's easy to get to know everyone and you'll also get the chance to work on a pretty wide range of technologies and on every different aspet of the product.
Cons
The biggest downsides are the pay and internal career progression.
Whilst the company has a solid foundation and good growth prospects, it only has a few major clients who provide most of its income. As a result, if there's been a setback for the company as a whole then it's not uncommon for salary increases to be delayed or deferred which in turn means that your salary can end up rising lower than appropriate for your level of experience - the salaries aren't bad as such, it's just that sometimes you could end up getting paid more for doing the same job elsewhere.
And because of the small size of the team it's also the case that room for internal career progression is somewhat limited. You can go from junior developer to a regular developer of varying degrees of seniority and that's about it unless you're able to make the jump to architect.