Honestly, I don't find that the sets are that competitively priced. They usually end up being the same price or sometimes slightly more than buying the bottles individually, and alot of times with the sets you end up with a bottle or two (or more) that you may never use, which results in the colors you would use actually ending up costing you more.
Which is why I tell people to just buy the colors they want, and don't bother with the sets unless they have colors in them that you just can't get individually.
A good example of a set like that is their new German ISAF color set, 8 new colors, none of them currently available separately, and only 2 out of them that I believe will end up as colors that will be available separately at all.
I carry the entire Model Color, Model Air, Panzer Aces, and Primer line, as well as their Pigment line and coming soon their line of new washes.