Ventajas
I worked here for two years and loved it. Firstco has a great spread of technically-strong engineers and project managers across key systems engineering disciplines. A lot of people working there have stayed 10+ years and as a result it's got a very friendly and relaxed atmosphere. Those wishing to go full-blown technical can get the opportunity to consult, bid, design, develop and deliver SCADA systems, PLCs, communications networks, PA/VA, CCTV, and a whole lot more. It has been one of the few companies I've worked at that genuinely seems to care about their employee's career aspirations and tries to give them the best chance at fulfilling them. The management is very approachable and always available for a chat about the company and potential upcoming projects you might be interested to work on.
Desventajas
The work can be very documentation-heavy at times which is boring for most, this is the nature of the industries Firstco works in. If you're an engineer who hasn't learned the importance and necessity of good documentation you will likely struggle.