Pixel King Pro wireless flash trigger is the 3rd generation of Pixel's TTL flash trigger. The design has been significantly improved and optimised. It has a big increase in range, now stated as approximately 300 metres which is a big improvement in reliability, especially when using TTL functions. The Pixel King Pro features a metal frame structure and a better software/hardware architecture, it offers a more stable and reliable user experience. The built-in user interface provides the ability to instantly see and access all the remote flash settings and controls, it's very useful when you need to change something quickly. Unlike the previous King triggers, the hot shoe pass through function is now enabled. The TTL pass through hot shoe allows you to use a flash mounted on it in TTL mode or manual mode. The Pixel King Pro is a transceiver so the unit can be used as either a transmitter or a receiver. The King X is a receiver only and can be ordered separately. The Pixel King Pro has an elaborate metal frame inside the plastic case like some high end cameras. There's a 1/4'' threaded bracket mounting on the side of the case, which is useful to mount another accessory or to mount the trigger on a L bracket. The Pixel King Pro has a shutter release function but you need a compatible USB cable to use it. You can trigger more than one camera at the same time using the USB cable. The Pixel King Pro and King X both have a USB port for firmware updates, so future cameras and flashguns can be supported with firmware updates.