Well I don't own any but I can tell you what I've read about them in other forums:
you must use them very VERY sparingly, they are crazily pigmented so you don't need much, pick the tiniest amount and build up if necessary.
They are not intended to be bases but I think it might be ok
They are grease paints so underneath them you need to apply something rather dry (eyeshadow base would be fine) and you MUST set them with powder, otherwise they will crease
You can also mixt it with clear lip gloss or anything you imagine!

I think I'm going to give them a try. MUFE has one nice pallet (they do not sell it at sephora) with 10 colors.