I own an original copy of this movie on VHS and a copy of Walter Karig's book of the same title. They are both little treasures and should be enjoyed when they are available to you.
Karig's book is a satirical little allegory and ends in a manner quite unlike the movie. I don't want to give away the ending of either, but I can assure you that you will enjoy reading the book even if you have already seen the movie (and vice-versa.) I will warn you, though, that the ending in the book is NOT necessarily a happy one.
As for the movie, it is indeed a departure from the norm for William Castle, but he dabbled in comedy in several other movies, so it is not THAT out of character. After all, the movie deals with what are essentially supernatural forces.
Contrary to what some other reviewers have written, I would argue that this move is much closer in tone to Disney's "Absent-Minded Professor" movies. There are the usual bumbling academics, the sexy-but-safe women, the well-meaning but suspicious Federal agents, the vaguely- threatening-but-incompetent foreign agents, and the likable and innocent hero. When the day is done, the hero defeats the villains, the self-righteous get their comeuppance, the girl gets the guy, and the "secret" is lost again...maybe.
The FX are about average for B-movies of that period. As a kid, I was astonished, but they definitely show their age when I watch it now.
I really think that kids today would enjoy seeing this movie. Give it a chance, if you get one. This is one rare movie to find on tape.
