I've never even heard of those books, hep. Someone bought one of those Fitzwilliam Darcy books for me and I HATED it! I had the same reaction to the GWTW sequel. I feel like screaming at those authors to get their own characters! I also feel that it's disrespectful to those great authors and their legacy to try to capitalize on their talent and fame.
I'll be on the look out for the Stephanie Barron books I don't have a problem with the concept. Historical fiction is one of my favorite genres.
ETA: LOVED Cold Comfort Farm! It's also a rare exception in that I can't decide whether I like the book or the movie more.