They have the advantage that you don't have to mix any colours, so there's easier consistency, but otherwise I don't see any benefit over old-school oil washes (oil paint thinned with white spirit), which are both cheaper and more flexible. Plus, the AK enamels' working time is less than with an oil wash.
I doubt that I'll be using the two that I have very much, and I won't be buying any more.
I made this textured colour chart to show me just what they're likely to look like when painted on to a 3d surface. The texture in this case is an acrylic wall filler, sealed with a couple of coats of Vallejo white surface primer.
The glazing medium I used is just a 50/50 mix of Vallejo flow improver and Golden liquid acrylic matte medium. I should probably have done a 1:5 ink to medium panel as well, but I didn't, so there it is. Maybe later.