https://web.archive.org/web/20140627115737/http://www.chesscafe.com/text/hansen99.pdf
http://www.gambitbooks.com/pdfs/Mastering_the_Chess_Openings_volume_1.pdf
http://www.gambitbooks.com/pdfs/Mastering_the_Chess_Openings_volume_2.pdf
https://web.archive.org/web/20140626220240/http://www.chesscafe.com/text/hansen117.pdf
http://www.gambitbooks.com/pdfs/Mastering_the_Chess_Openings_volume_3.pdf
https://web.archive.org/web/20140627070808/http://www.chesscafe.com/text/hansen137.pdf
http://www.gambitbooks.com/pdfs/Mastering_the_Chess_Openings_volume_4.pdf
https://web.archive.org/web/20140626173432/http://www.chesscafe.com/text/hansen128.pdf
http://www.gambitbooks.com/pdfs/FCO_Fundamental_Chess_Openings.pdf
I am curious of others opinions of these two books (well, one book and one set of four).
I bought FCO for a couple reasons. First, it's one volume and cheaper. Second, it's one volume and from what I could see Watson would often say something like "see volume 2" while covering a line, due to transpositions (which is a bit annoying). Third, FCO is a bigger book, such that it seems to have as much material as two or more of Watson's set. Still, I wonder. Is Watson's set in any significant way more detailed, more current, more correct, etc.?
What do people think?