Does anyone use AN glass on both sides of the negative? I still get occasional Newton rings and am considering switching out the lower plate of clear glass for another AN piece.
Yes, Howard Bond does, for example, and his prints look pretty good, although his enlargement factor isn't that big. Some of the new films, such as 100 Tmax and Acros, have very shiny emulsion sides which can cause Newton's rings with regular glass.
Anti-Newton glass has a fine texture which breaks the interference pattern of light bounced between two shiny surfaces. You'd think that having a textured piece of glass in the optical path would be a no-no, but it isn't always so.
For example, I have a Screen Cezanne scanner, a huge professional flatbed that cost about $30,000 new. It's main scanning bed had a very fine anti-Newton texture. Convinced that this would cause a problem, I build a scanning bed using optical glass. At 5300 spi, I can see no difference in sharpness or detail between scans made with the two beds at 100% on my computer screen, which would equate to a gigantic print size.
One thing to be aware of is that the texture size of anti-Newton glass varies from supplier to supplier, and some might degrade the image. The only way to know if it'll work for you would be to test it.