Pros
Trayport has a long held reputation for hiring great developers and QAs, and during my time there I definitely found that to be true. Working with talented people is one of my main requirements in a job so I found that very satisfying at Trayport. There were some interesting projects to work on as well and it always seemed like we were on the lookout for appropriate new technologies to use. It was a definite CV builder. The social culture at Trayport was great too. Spent a lot of time at the pub after work and the monthly events they put on were always fun. Met some great people who I still see regularly.
Cons
All the pros I mentioned are unfortunately cast into the shadows by one major issue at Trayport: management. Like I've said, pretty much everyone on the ground (doing the actual work) does a fantastic job (although I've been hearing from people still there that recruitment quality has dropped off). Trayport has an uncanny ability to hire absolutely appalling high level management. I generally view the top-brass as reasonably innocuous, it's the level just one below that are the issue. Not only do they seem consistently bad at their jobs but they're arrogant bullies who undermine anyone who they take a personal dislike to (i.e. if you disagree with them on any point whatsoever) and who blame developers/QAs for absolutely everything. There's certainly a feeling at Trayport that management view developers as a necessary evil, which is ridiculous. This was the case when I was at Trayport (leading to them losing an incredible number of developers over a 6 month period) and although I heard it got better for a while it seems to be the case again (possibly even worse now by the sounds of it). By far the busiest team at Trayport are HR with constant recruitment and exit interviews. Clearly that's not right. If I were a potential candidate considering Trayport I'd stay a million miles away. It's just not worth the hassle. Oh, and to top it all off the pay isn't very great, certainly not industry standard.