It is a little toxic but it is a common household cleaner and not a horrid industrial pollutant, so with a little care, it is fine. I add it to paint and paint it on without any problems.
I used the etching to produce the clouds and water effects. I am currently looking to do some prints exploring the range a lot more as I haven't used it on subsequent layers. I am looing to explore using the etching for the background and the carving for the foreground (Approx) to produce a subtle depth of field effect. I like the contrast between the etched and the carved. With the etched marks, there is some variation dependent on the thickness of the ink layer etc. because some of the marks are quite shallow. This creates some interesting variety and in places a sort of half tone effect.
I love the ideas of combining intaglio, tonal transparency and perhaps etching. Although I am love the graphic quality of lino, I am interested in it's potential for a more painterly result as well.