The larger unit is designed for a variety of uses, the Inspire, X5 and X5S cameras only being part of those.
You can buy two variants of the big DJI FOCUS unit (the big one), one has a motor with a gear and strap which can be used to remotely control lenses on big cameras - either cinema or photo. the strap has teeth on it and it's fastened around the focus/zoom/aperture ring on the lens. The motor then couples to the strap (usually by fixing to some rails under the lens) and drives the focus/zoom/aperture ranging mechanically. The DJI Focus unit is used to control the motor remotely - it can do that without needing to be transmitted via the Drone Remote Control. This variant usually found being used with the Ronin and something like the M600 or S800/900 and a DSLR camera.
The second variant is just the Big DJI Focus unit itself (without motor or gear straps) - it can be coupled via a cable to the I1 controller and used to operate either focus and aperture on the X5 series cameras. You can also connect it to the I2 controller (using a different cable to the I1) and control the X5S camera in the same way.
There are a few other features to the DJI Focus unit that the smaller DJI Focus Handwheel doesn't have like electronic preset position memories and the ability to change between focus and aperture adjustment using a button on the controller.
The smaller DJI Focus Handwheel connects in to the remote controllers using a smaller (and different) cable to it's big brother, and operates either the aperture or focus on the X5 and X5S cameras - it's a smaller, lighter and cheaper setup dedicated to those cameras and can't be used with the motor+gear strap setup. It also has to be coupled up to the camera or the remote controller using the cable. It doesn't have electronic presets and you need to use DJI Go to switch between Focus pulling and Aperture adjustment.
Basically, unless you're going to fly a bigger rig with some other makers camera/lens on it, you don't really need to pay for the big focus unit. If it's just DJI & the Zenmuse X5 series cameras, then the smaller Handwheel should do you
Think that lot makes sense and is right! It is a bit confusing at first!!!
