Synchronous video
This is an analogue mixer, so all input video signals must be synchronised together. Your sources all need to be genlocked, or externally resynchronised if the sources can't be genlocked.
If you're resynchronising every input source, you may want to consider getting a different mixer that can handle random unsynchronised video, all by itself. It'll save you buying a lot of synchronisers, but lose you the advantage of having individual control of each source (many digital/analogue hybrid mixers only let you control the A and B buses, directly). And many digital/analogue hybrid mixers glitch every time you switch between non-synchronous sources.
Composite video
Although this is a component video mixer (primarily luminance, and the two colour difference signals, but three of the inputs can be RGB, instead), it is possible to use it with composite video inputs.
If you put composite video into the Y inputs, the full bandwidth of the video is passed through. You'll need to use the mixer's composite video outputs, as only those mixer outputs will re-insert mixer sync and burst into the output video.
The mixer's Y output will have sync without burst, and will only be of use to B&W preview monitors. The colour difference outputs will have no video signals, except for when using the internal colour generators (colour bars, background colours, and matte generators for key fills and wipe borders).
It doesn't split apart composite video into components, so you can't use it as a transcoder in that direction. But it does encode component video (externally suppled, or internally generated) into Y/C (S-Video) and composite video outputs. That's just simple PAL, or NTSC, colour encoding.
Since the mixer isn't designed for composite throughput, there will be an uncorrectable phase shift between the program and preset busses. The second video source will have a sub-carrier error during transitions, that will suddenly disappear when the transition completes, and mixer switches from effect video to just the program bus. Also, the preview monitor output will always be out of phase, so you can't use it to line up sub-carrier phase.
And why would you want to use a component video mixer for composite video? It may well be the only mixer you have to hand, and you may not have component video sources, such as cameras without CCUs.
Irritations
The colour matte generator has the most peculiar method of setting colours, rather than RGB pots (my preference, as 0 to 100% RGB controls cannot generate illegal colours); or a red versus blue vector joystick (which easily produces illegal colours if not properly matrixed); or hue, sat, and lum pots (which, again, easily produce illegal video signals if not properly matrixed); it has a joystick which slowly spins the hue when moved in one axis, and slowly ramps the saturaton up or down when moved in the other axis, with a luminance pot. Though it does have a nice digital display of hue, saturation, and luminance values, where the luminance is stated in IRE units, but I don't see what units the other values are represented by, there is no quick way to select any particular colour, on the fly. You'd need to labouriously set up the colour, then store it into a memory preset. And you still need to be monitoring the output with a waveform monitor and vectorscope to ensure you don't create illegal video.
It's really a post-production desk, there isn't the preview facilities needed for live production, such as: A completely independent preview switcher. The ability to set up a split screen, then fade it on and off. No pattern limits, so you could auto-transition on a wipe, and have it stop part way at a predetermined position.
Faults
Without access to another mixer to compare, I can't tell if this is a technical fault with our mixer, or a design fault with the KM-3000, but the program/preset cut button does not switch the tallies as it switches the video.
e.g. If you had camera 3 on-air, and camera 5 being previewed, then pressed the cut button, camera 5 would go to being on-air, and camera 3 would go to being previewed, but the camera 3 tally will still be erroneously lit up.
Pressing the auto transition take button does mix over to the preset video, and switch the tallies, properly. Likewise, the tallies work correctly when directly switching inputs on the program bus.
And there's a few other tally faults of lesser importance: Using the downstream keyer doesn't turn on the tallies for the associated key source (e.g. If I'm downstream keying input 7, then the tally should go on for source 7). And fading to black doesn't turn off all the tallies, as it ought to do.
Tallies appear to be completely CPU controlled, and would probably require new firmware to change the behaviour. That or a complete new circuit which monitors the lamps on the program and preset busses, and the transition control (to be able to tell when to use tallies from both preset and program, or just the program bus). I was considering designing such a circuit, but then we stopped doing analogue recording.