Pros
American Express (UK) looks after its employees extremely well. Type of health insurance, support and other benefits can be one of the best in the industry. Company can contribute up to 11% pension if you contribute 7%. Not many companies do this. They would pay good bonus and pay rise if you have done well in your performance ratings. Also, company performance is taken into consideration when adjudicating bonuses. Flexible work pattern (working from home) exists and some people can apply to work from home 100% time - sometimes it is granted. There are opportunities to learn additional skills and you'll be supported by your manager well in this.
Cons
Beware of various bands within Amex. This is somehow kept secret to outsiders. Ask the recruiters - what is the job band for the role that you are applying. It (job band information) won't appear in public job board - only available in internal job board. If you have several years of experience, you still may be applying for Band30 which is a junior position. A senior (manager) position is Band 35. It is almost impossible to get promoted from B30 to B35 unless you are engineer (software developer). B40 are called Directors. B45 starts at Vice President (4). VP III, VP II are also there. B70 is called usually Senior Vice President or Country Manager. Next level up is Executive VP. Next is President and then C roles. There is no automatic progression or promotion within Amex. For each role, you have to apply and unless you have something called great "networking", i.e. you have the sponsorship of influential people, you can forget about promotion. There may be exceptions but this is how it generally works. It does not matter what is your annual performance - best performance won't give you promotion. The only way is - you impress your leader by agreeing to everything they say and then they internally open a role and promote you. If you are not in the good book of your "leader" i.e., line manager, nothing will happen and you may have to look for jobs elsewhere if you want to be promoted or earn more money. Some "leaders" can be jealous and try to block subordinates to be promoted as best they can. However, American Express should not be judged by the bad behaviours of minority (leaders), but you still need to be mindful of this situation.