This book’s Wikipedia entry contains a section called Reception that covers it pretty well (emphasis mine):
Some reviewers have criticised the book for encouraging its young readers to partake in activities that could result in injury, although there is a liability warning below the copyright information, as well as for promoting gendered stereotypes.[5] Others have praised it for helping to counter “PlayStation Culture”[2] through its promotion of outdoor activities and games.
Activities that could result in injury? Uh yeah, that’s the whole point. This book was so awesome for me as a kid. I reread every single page and did just about every single activity the book mentions for years, probably from the ages of 8 to 12. Camping, whittling, navigation, knots, flags, games, history, making weapons, you name it, everything fun to do indoors and outdoors seemed to be in that book. They even taught you how to do the paper marbling effect that was on the front page of the book.
It was completely empowering, and rereading the opening statement of the book now, I realize how profound an impact this book actually had on my intellectual and emotional development.
Don’t worry about genius and don’t worry about not being clever. Trust rather to hard work, perseverance, and determination. The best motto for a long march is ‘Don’t grumble. Plug on.’ “You hold your future in your own hands. Never waver in this belief. Don’t swagger. The boy who swaggers—like the man who swaggers—has little else that he can do. He is a cheap-Jack crying his own paltry wares. It is the empty tin that rattles most. Be honest. Be loyal. Be kind. Remember that the hardest thing to acquire is the faculty of being unselfish. As a quality it is one of the finest attributes of manliness. “Love the sea, the ringing beach and the open downs. “Keep clean, body and mind.’”
—Sir Frederick Treves, Bart, KCVO, CB, Sergeant in Ordinary to HM the King, Surgeon in Ordinary to HRH Prince of Wales, written at 6 Wimpole Street, Cavendish Sqare, London, on September 2, 1903, on the occasion of the twenty-fifth anniversary of the Boy’s Own Paper
As for gendered stereotypes, I remember they had one small section called “Girls” which seemed odd to me even at the time, and reading back, certainly does contain stereotypes you would only hear repeated by an old uncle today, or probably great-uncle. However, this is one page among over 200, and the general gist I remembered was essentially - be nice, listen, don’t be vulgar, don’t worry too much about them, and be yourself.
My sisters had The Dangerous Book for Girls, which I remember didn’t cover nearly as many cool topics, and which they didn’t enjoy nearly as much as I enjoyed mine. If I ever had a daughter, I would definitely just give her this book instead.