Yo I'm currently applying for the economist bit, got as far as the FSAC two years ago but decided it wasn't what I wanted to do at the time so cancelled my appointment. Somewhat regretting that now but c'est la vie. Interested to hear how other economists are finding the online tests? I was fairly happy with my practice scores, just did the verbal for real and got an error message. So we'll see...
As far as advice goes for the Economic assessment centre goes, I would suggest a fairly chilled out approach, have a good read of Begg and also of Varian, and put in a good chunk of time on the topic you are set. I know for a fact my reading wasn't quite wide enough for my topic, as they mentioned it in my feedback (which you can request after). I still got through but I imagine competition is going to be extremely fierce this ear.
I think stressing out about it too much killed a couple of people I know who attended an EAC, so lots of deep breaths!
Good luck guys!