Pros
Working for AI you will have some exceptionally talented and dedicated colleagues and have the chance of working on interesting and challenging projects, for clients that you'd be unlikely to get at other firms. However, the talent is being driven away by management who value conformity and mediocrity over creativity and excellence, and the commercial clients have been driven away by the imposition of the parent company strategy.
Cons
Whilst once there was an interesting and large variety of clients across all industry sectors the counterproductive name change from Detica to BAE Applied Intelligence brought with it a retrenchment into the core defence business and almost all the commercial work disappeared, with no likelihood of ever getting any more. Over time the Big Defence Consultancy has subsumed or killed everything that made Detica such a fantastic company and now it is another soulless consultancy run by suits. You could spend your entire career on a client site, never seeing your actual colleagues. Most of the work you will made unnecessarily more difficult than it need be by a combination of excessive and inappropriate process, overmanning, toxic clients, and ineffective managers who singularly fail to manage their expectations. It is an epidemic: budgets for creating the actual product will be squeezed so that hundreds of project managers can be parachuted in to a client to hoover up all the money. Very few of these managers seem to offer any value whatsoever. In an effort to claw back some profit development will be outsourced to inexperienced and incorrectly-skilled juniors (in increasing numbers) rather than the talented people who could actually make things succeed. Management is very top-down and the fee-earners have no say in what happens to them. A bad word from a manager can destroy a career. Staff are lied to, mis-sold onto projects, set up to fail and then screwed when it comes to bonuses and pay rises. Reviews are a box-ticking exercise designed to prevent anyone ever making career process. It doesn't matter how good you are, how hard you work, how many millions you make for the company or how many of your objectives you hit. Career progression depends entirely on who you know and how little you rock the boat.