I’ll share my experience. I was basically looking for customers and projects. I had my CV on Linkedin, Freelancer, Elance, and was checking out Odesk. Someone recommended me Toptal, so I sent an email and received the invitation to do the automated test. I was sceptical, is this worth it? Or will I loose my time.. my friend insisted, as the rate is very good and you will not get clients like that on another freelancing site. So, I invested the time, after some hours learning about the codility tests, I did the test. Followed by another interview with with an engineer while coding and sharing screen. In less than 15 days I started a part time job (earning more than I was earning before with a full time job for another US customer), then other projects came, and have been there for 3 years and never stopped.
About the rate, I shall not share my rate here, but I can tell that I'm in Argentina and I earn more than most of the developers from the US, actually many people I know and are with Toptal from my region got offers to go to work to San Francisco and rejected them, because they prefer freelancing and the freedom which it brings.
You’re milage may vary, but I am happy to be working with Toptal.