What other certifications exist?
Well, I just took the advanced tests (in beta) last week at the Dev Days in München. Vladimir was right, a lot of the questions were about making statements on a piece of code. That was better than what I remember of the Essentials exam last year. Still, there were a few questions that required knowing something by heart that I thought was something that you'd normally just quickly look up in the docs. I can not be more specific on this public forum (you have to sign an NDA on the contents of the exam). Still, this happened less in the advanced exams than in the essentials one, and I don't think it is much of an issue if you have sufficient exprience with Qt: you'll make it anyway is my idea.
P.S. Turns out I was right before when I suggested I should start studying for this years dev days :-)