Pros
Good experience, you can learn how to interview, do practical research, casework, and actually make decisions. The work itself - interviewing asylum seekers, researching cases, casework, writing decisions - can actually be interesting.
Cons
Effectively you're a junior immigration solicitor, but on less than £25k and with 2-3 weeks training. Main cons: the lack of consistency and honesty in management, the sales targets culture to getting decisions done, the literally impossible targets, the endless feedback sessions by consultants that literally never gets listened to, there are very limited progression opportunities and most of them go to the managers' pets and brown-nosers, also the bullying can be really bad - manager's following you into the toilets to ask why you aren't at your desk, demanding you come into the office for no reason, pestering you all day to get a decision done without offering any support to help progress it.