Yes, and they can be mixed with either solvent or water, but not together. Using solvent seems to give a very flat acrylic type finish, while while water leaves a flat to very slight, almost imperceptible, sheen. Roger found they were a rather too oily, but I have not had that experience with the tubes I have (W&N Artisan). In fact just the opposite - some are quite thick when squeezed from the tube.
As you say Alan, some people don't like them, but I like the combination of being able to blend them and a quick drying time, as well as being very easy to use. They have become my preferred medium. (just can't crack the washes for highlights and shadows with acrylics).
Chris