I use vallejo Acrylic Artist Color , vallejo modelcolor, citadel fundations, washes, old citadel paint and inks, and even mix all of them to see if works some weird chemical reaction.
IMHO the quality of some colors of the Vallejo fine arts acrilyc are much better than their equivalent in other ranges, but this is merely a matter of personal taste.
The back of the tubes and their color card include a samll checkbox to evaluate the color opacity, a kind of opacity guide.
On the back of the color tube you can see a circle or a square , full black means the color is dense an will cover nicely the surface, half black and half white circle means the opacity capability is lower than the full black circle, so, bad for minis except if you are looking for some kind of transparency effect (nothing to do with GW inks or washes) if the circle is full white avoid it.
But that guide is not 100% secure, sometimes color marked as opaque are not enough for miniature painting, maybe they cover enoug for canvas, but not for minis.
if you go here
http://www.acrylicosvallejo.com/gb/downloads.htmlyou can see the Acrylic Artist Color card, on each color you will see a small square, it's the stuff about the opacity, but even some colors marked with a black square when used can fail, for instance,
I have the #605 Cadmium Red Medium is an awesome intense red very dense an 100% opaque, next there is #402 Naphthol Crimson that is much less covering, an next it is #504 Cadmium Vermilion but despite is marked with a black bullet his opacity is very crap similar to #402.
Until a certain point is a matter or error/success test, it's fine you have an use for the less covering ones.
edit: by the way, about the tutorial you linked, this blog is not from a LAF member?