Richard Poynder has published "Emerald Group Publishing Tests ZEN, Increases Prices: What Does It Mean?" in Open and Shut?
Here's an excerpt:
So why has Emerald chosen to trial ZEN [Zero Embargo Now] with some of it library journals, what role did the LAG play in the decision, and what do members of the LAG feel about the associated 70% increase in the APCs of 32 engineering and technology journals?
In the hope of finding out I emailed Emerald and asked where I could find a list of advisory group members. It turns out that these are not publicly available.