Speedpaints are the Army Painter's response to GW's Contrast paints where the idea is that a single specially formulated paint allows a base coat, shade and highlight effect to be achieved in one application. There has been some controversy about the reactivation effect where overpainting or highlighting causes the speedpaint to bleed in with any water based paint or glaze. This video shows how to get around it and to use reactivation to produce highlighting effects.
Overall I have found that Speedpaints are great for bulk paining armies, which is what they are intended for, but they reward painting that keeps colours in the areas they are meant to be in as they are quite translucent so anything under one can show through.
Here are some trial pieces I've been working on.
Alternative Armies Sidhe (Celtic Elves) - using Crusader Flesh and Dark Wood. The flesh definitely works better over a flat white undercoat than something else I tried which was a pseudo-zenithal approach with a grey basecoat (AP Uniform Grey) with a white drybrush that I tried with the witches. I think next time I use Dark Wood I'll thin it with some medium as otherwise I find it a bit strong.
Frostgrave Witches made from the plastic set and Reaper Owl familiar. Crusader Flesh, Grim Black, Dark Wood, and Gravelord Grey used so far. I used my pseudo-zenithal technique on these but in future I'll use a plain white finish on skin areas.
Skeletons from Mantic and Oathmark in Pallid Bone, Dark Wood and Gravelord Grey. Reaper bones troll done with pseudo-zenithal and Orc Skin. I'm pretty happy with these particularly the troll.