Andrew has always given me a pretty good deal when it comes to buying Vallejo paints and as David points out, has the entire range so you don't have to go to several suppliers.
I think he got sick of me badgering him about MIG pigments and is in the process of becoming a distributor for those also.
This is my own personal opinion but I rarely ever use Vallejo Model Colour for airbrushing. Some love it, some tolerate it and some hate it... I am of the latter category. It does not matter what I dilute it with, what dilution and pressure I spray at I get fed up with it sputtering and being a general pain in the backside. Other brands spray flawlessly so I stick with them now.
However, the way it brushes on makes it the first choice paint for me. Before I started scale armour I exclusively painted miniatures and Vallejo Model Colour was always my go to paint. Great coverage with most hues and no brushstrokes.Great for applying chipping/weathering. Fantastic colour range if you are like me and only mix if you have to. There are a few colours that are well used and are handy for such tasks. The bronze and brass are nice metallics.
Some have had problems with the eyedropper bottles clogging but if you spend the time keeping them clean before you cap up for the last time the incidence is greatly reduced.
Finally, depending on the way you paint they have an inclination for the colours to split when diluted so need to be mixed regularly on the palette or used quickly by airbruish.