Pros
What this company does for its clients is absolutely tremendous and not matched by any other organisation, anywhere. It employs a hugely diverse group of people, who, on the whole are massively enthused and committed. Working with the medical people, who daily effect peoples health and well being in a huge variety of circumstances, is extremely rewarding. Management listen, and are always up for change subject to the price tag. and despite what some other people seem to think, you do get heard, its a fair place to work, and the London office environment is really hard to better. Their CSR program is with London Air Ambulance - what a fab cause! Values are good, and on the whole are "lived" - always some outriders though.
Cons
No business is perfect, and this one does not get everything right all the time - but it does try. As a privately owned and founder managed business, you need to get your head around what that means before you join, as that means its going to be different to a public quoted company. They need to work on their hiring and people side a bit more, to make sure they are true to what the jobs actually are, don't over cook them, and make sure the people settle into them well. Benefits are ok, but could be sharpened up a bit. Time at work can get heavy at times, but not constant.