Army Painter recently released their new line of Speed Paints. They make the same promise as Citadel's Contrast Paints in that they'll provide a base coat, shading, and highlight effects with one coat.
I bought a fair number of pots of the Citadel Contrast paints when they first came out but I was generally underwhelmed by the results when compared to just a regular base coat and wash. I also found that the properties of each colour of contrast paint varied quite a bit. Some were much more viscous than others and some had much more pigmentation than others. I found that it took quite a bit of time and experimentation to find out how best to use each paint (some required thinning to prevent coffee staining, some would work well with one coat while others required two or three) and, as a result, I wasn't seeing the promised benefits of ease of use and less time spent painting. Also, they're bloody expensive.
Due to my less than positive experiences with Contrast Paints, I wasn't all that interested in the Army Painter line but just happened to be in a local hobby store when the first lot of the new paints arrived. The owner offered to sell me a set a day earlier than they were supposed to go on sale so I bought a starter kit.
PROS:
Dropper bottles instead of pots and each bottle comes with a mixing ball.
Half the price of a pot of Contrast Paint
Uniformity of paints regardless of colour. They all seem to have the same consistency and level of pigmentation so it's easier to learn how to apply them.
Better and more even coverage than contrast paints. They apply more evenly and one coat usually does the job with less pooling and coffee staining.
Most colours seem to give a better sense of highlights and shadows compared to Contrast Paints (a few don't).
CONS:
The colour range is more limited than Contrast Paints and the paints included in the Starter Set tend to be very vibrant. This leads to more cartoony, high contrast looking models. Some people prefer this but I tend to like more muted, natural looking models.
Harder to control the flow when compared to Contrast Paints. The Speed Paint seems to get away from the brush more easily than Contrast Paints and will run along deep recesses past the point you were trying to cover.
They don't behave well when thinned with water. Contrast medium works fine as a thinner (I haven't tried the Army Painter Speedpaint thinner medium yet but I hear it works well) but water causes it to lose cohesion.
Can look a bit chalky or pixelated over some primers. I tried Vallejo, Tamiya, Mr. Hobby, Citadel, and Army Painter primers. These paints look best over Citadel Contrast primers. Oddly, they tend to look almost pixelated over Army Painter primers. Same with Mr. Hobby. Vallejo was OK but a little bit chalky looking compared to the Citadel primer. The paints had an almost hydrophobic reaction to Tamiya and didn't seem to want to adhere very well.
*The BIG ISSUE: These paints reactivate when they get wet, even if you've let them dry for days beforehand. This means you can't layer colours or even put a wash of a glaze over them as the Speed Paint will re-liquify and end up messily blending with the new colour. This means you have to apply a varnish layer after using the Speed Paints (and too much varnish will also cause the paints to reactivate and possibly flow past where you applied them).
VERDICT:
I like them better than Contrast Paints and I can see using them for batch painting up lots of generic figs for tabletop fantasy games. Whip up a bunch of zombies or goblins or skeletons in no time. I wouldn't use them for more unique minis though as you're going to get tabletop ready results from these paints, not quality jobs. They also wouldn't be much good for vehicles or anything with a lot of large, flat surfaces.