Jotun call it multicolour machine, not sure what nippon call it, every machine is maintained by their respective manufacturer, nippon will be maintain by nippon , jotun by jotun, there is no cheap or expensive machine

You go to the shop tell them the colour code and also the type of paint you want, when they key in the info in machine they will be able to tell you the price

The colour is mostly accurate, if you buy the same colour but from different shop, and you found that the colour is different side by side then you can try to contact the paint manufacturer for warranty, but I'm not sure how is the process here

For nippon I find that the painted colour is very different from the catalogue, while Jotun painted colour is always very closely matched to the catalogue, but nippon has better wood stain colour, I like their hydrowood wood stain series, I haven't tried Dulux before so no comment on that brand

If you want to choose colour that is not in the catalogue, you can go to shop and request for fan deck, nippon has 1000 colour fan deck, while Jotun has 800 if I'm not mistaken, but choosing from fan deck is risky because you can't take the fan deck back home to match with your house lightning condition