Let me preface this by saying that your experience at FAST will be totally dependant on the project you are on. I am just speaking from my experience, you might not encounter these issues on every project site.
-Lack of mentorship, training, and documentation. Even though coworkers are generally eager to share their knowledge, the learning curve at FAST is incredibly steep due to the lack of documentation and mentorship. You are expected to be working with the client and solving problems from day one (which is good), but you are not given the tools you need to do this in my opinion. I guess FAST has decided that the ‘sink or swim’ approach is the best way to bring new hires on board. There is a training period when you first start, but it was not very useful in my opinion. It was fun though. This may have been improved since I started.
Eventually you'll get the hang of things, but this can land you in some real hot water because you are modifying and developing key components of software without having any idea what you are doing. There have never been (in my two years of experience) any code reviews or performance reviews, so you won’t know if you did anything wrong until it figuratively blows up in your face. There is a lot of pressure to get things done fast, and an emphasis on quantity over quality. This is a good way to dig yourself into a hole with no way out.
-Lack of growth. The ‘development’ you’ll do as an Implementation Consultant (IC) is mainly configuration of FAST's off-the-shelf software. You’ll spend most of your time learning the business process (for example: how sales tax is calculated, or how tax returns should be audited) from the client. The solutions for these problems are built using proprietary data structures in Visual Basic. You won’t use arrays for example, since FAST has built their own version. The IC position is very light on the coding, and the coding you do is very limited in it's scope.
Most of these FAST-specific data structures are undocumented, so you end up spending a lot of time trying to work around something, only to find out that someone had already added the exact functionality you need, but didn’t think to write it down anywhere. In training, we were actively discouraged from adding comments to our code by the CEO of the company. I found that odd.
-FAST has good reasons for using a proprietary data structures and keeping much of their system obscured and locked down. Having their consultants configure existing software rather than developing from scratch shaves years off of rollouts and makes the process extremely efficient. Because of this, FAST leads the industry.
You benefit from this by being paid well, but if you are looking for a technical position where you can learn new technologies that are relevant to the software industry, as well as sharpening your development skills, this is not the position for you. I cannot stress this enough. This is not to say that FAST is a bad company, but it is very different than most software companies. Just make sure you know exactly what you are getting into. Although FAST has great Glassdoor ratings and many awards, it is most definitely not for everyone.
I know several employees who are jaded because this position is sold as a development position where you can find your niche and build code that improves people’s lives. If you end up on the wrong project, you will be stuck cleaning up other people’s messes with very little opportunity to get out. Just be aware of what you are getting into if you take this position.
I am not sure if I regret taking this position or not. But it is hard to get out once you get in, and any tech skills you have going in will atrophy quickly unless you are working on projects outside of work. But will you really want to do that when you are working 11 hour days through rollouts?
Also, don’t work for fast if you don’t like to drink. It’s hard to fit in if you don’t like to drink.