If yes, what do you think about them?
No but what is really special about them?
Okcoin has the most liquidity compared to the other future platforms. You can use up to 20x leverage. It's really where you want to be trading futures.
Well they don't really have a platform, just an exchange, with trading through the website. If you don't have custom software platform for trading then trading with 10 x or 20 x is somewhat asking for problems.