As an (ex) employee of the aforementioned company, I feel I should mention that whilst it is possible to make up a damned good colour match, the computer system containing the 'formulas' (the quantities of each component part of paint) in some cases has multiple slightly different shades for what is the same colour - some suffixed with different letters or numbers, indicating a slight tint in a particular colour direction, supposedly to cater for fading/bleaching, but getting a right match for some colours, especially those which are prone to fade or get bleached in the sun is quite tricky. I recall being asked to mix a Ford colour to which there were 10 slight variations of the same black shade on the computer!
Its nice to have a bit of time to mix it up as well given that its 'mixed' by hand, not by machine as people always seem to think! Some of the formulas require some minute amounts of particular components so to follow it exactly to the nearest gram you're best adding it slowly drop by drop. When I worked in Halfrauds, we always had some customer who needed it mixed in 5 minutes and whilst it can be done, I always preferred to take a bit more care and really mix/stir it thoroughly!