It's mostly just marketing hype; all boxes are almost as quick and easy to fit to roof bars, whether or not they have 'quick fit' systems.
As a rule of thumb, the quicker the box is to fit, the more space the fitting system takes in the box, i.e. the less space there is for the luggage, although the KAMEI system is relatively low profile.
Bear in mind also that many people leave their box permanently fixed to the roof bars, so fitting time is irrelevant. And also ask yourself the question, "If I take my box on holiday 3 times a year, and the slower but low profile U bolt fittings take an extra 2 minutes to fit each time, does this really make any difference?"