The ML-L3 on the lower priced dSLRs require the camera to on with the AF and light meter running (big time battery drain), only operates on one control channel, only trips the shutter, and the receiver for the IR signal is fixed to the camera body. Multiple shooters can interfere with each other.
The ML-3 consist of transmitter and receiver. The receiver connects to the 10 pin accessory port and can be remotely located with the use of an extension cord. The receiver is also wired in parallel to the shutter control switch and does not need the camera to The system supports 2 control channels so more then one photographer at a time could use the remote an not interfere with the other. The transmitter has a 2 stage shutter release so the camera will wake up and focus just like pushing the shutter release half way down and a full depress is required to trip the shutter. There is a "shutter delay mode" that allow the mirror to swing up and a delay to allow the vibrations to stop before the shutter is released. The intruder trip allows the transmitter to constantly send an IR beam to the receiver and only trip the shutter when the beam is broken.
By buying a cheap programmable TV remote I can have an ML-L3 replacement for less then $7.00.