Not many folks have had the courage to buy those Pixel Knight things yet. They appear to work, after a fashion, but have some strange operational issues and are not very reliable. I wouldn't, but it's your money.
You can hack remote remote HSS and second-curtain sync pretty well by hooking up an RF-602 to an optical slave, for a tenner. You just need a suitably enabled flash on the camera to trigger it.
There's a new Yongnuo ST-02 clone just out, which appears to be very good. Better than the Canon version and much cheaper at around £100 on ebay. It's still a bit of an unknown quantity but I think probably worth a punt.