I am not one to complain about Logos' promotional methods, but this seems to be a bit over the top.
While I'm not that interested in the works of John Darby, I thought it might be helpful to get the free book setting forth his views on Genesis through 2 Chron (If he follows the Jewish order, this would be the entire OT). When I used the Logos home page to access the offer, it ended up showing an upgrade to L5 Silver in addition to the book. If they wish to say "Free book with the purchase of an L5 upgrade", that is their right and I would have no complaint. This, however, is a bit sneaky and unlike what I am used to experiencing with Logos.
BTW: I'm waiting for the free engine and crossgrade since I plan to add only those works I want which doesn't include homiletical material, sermons, counselling and numerous commentaries of no interest to me.