There was a big article on using these in Military Modelling a while back (Vol. 30, Issue 13 in 2000).
They can be used with water or as regular oil paints. Mixed with a little 'regular' oil paint, they stay water mixable. I think if you have more than 30% or 50% regular oils, then you need to use oil thinner etc.
The paints are very thick compared to regular oils, I found. I have the Grumbacher and W&N ones. I've used them a bit. I tried painting a whole figure in the water mixable oils, but didn't have enough colors to finish it all that way.
They do thin and clean up with water if that's what you are looking for.
Andy