I agree, your etches are amazing, Iain. So clean!
If my memory is not failing on me, I did reverse etch 9 times, plus a mix of "regular" etch and reverse on the same design (a big muff based on the original artwork and another one I didn't got the layout to fit the box yet), all for 1590A. They're indeed hard to get a good result, but on the other hand the regular etches are hard to keep clean the parts you don't want to be etched.