I did not realize that history about Eric Schiller 
It makes sense now. I'll definitely explore more alternative options to going against the French defense then! I thought it was a nice little surprise though for certain and was fun to play in a casual setting, that's for sure.
Holy crap! Schiller is even a plagiarist!
https://www.chesshistory.com/winter/extra/copying.html
Honestly, I only got the book and started reading it because of John Watson's co-authorship and my understanding of his expertise with opening theory. I hope his input has somewhat moderated Schiller in this book but I didn't realize all of that about Eric Schiller
Actually, I think the thumbs up is for white as it is divided into three sections and six parts. The first section covers unsound openings for white/black, the first part for unsound white openings, second for black openings. It flips the colors for each part. Second section is ugly openings.
Yes, black can play against it, but it is marked as sound for white. Hence, their lines are for giving black equality against a more ugly but playable white opening.
And actually, it does not surprise me. You must be young and not know the history. Eric Schiller, now deceased, was a TERRIBLE chess author. He never had a title above National Master ( that is well below FIDE master) and he churned out books one every 2 weeks. They were all horribly written.
Just to give you some perspective:
In the intro to Standard Chess Openings, he mentioned that some openings got more coverage because he know them better. What are you doing writing a book on all standard openings if you do not know half of them?
Also, same book, in the Section on the Semi-Slav, Botvinnik Variation, he uses a game between Ivanchuk and Shirov from 1996 (Pretty popular game, it is also Game 1 in Sadler's book on the Semi-Slav). You can find it in databases too. It is 35 moves long, and White's 21st move is a Queen sac on g7, and Black's 23rd move is 23...d4.
Sadler, and any other author not named Schiller, gives this move either a ? or a ??.
Schiller? !!. And guess what, nowhere does Black make a subsequent mistake according to Schiller, and after 35 moves, it is 1-0.
And now that I looked at the authors you mentioned, I do not believe Jack sh*t that book you mention has to say. Watson is only listed for name recognition. Schiller wrote the book.
I have spoken to Jacob Aagaard in person more than once. He would know a little more than you or I do as he is a GM and the co-founder (with John Shaw) of the publishing company Quality Chess. When you see 2 authors, one is a ghost writer, and the less recognized is 98 percent of the time the writer of the book. The other might write the introduction.
So yes, I believe nothing that book has to say. Wing Gambit is dubious at best, and after 4...d4, Black has a slight advantage already!