I'd never really thought about it, but most books about dating, sex, and relationships for teens are aimed primarily at girls; this is one of the first specifically written for teens who identify as male. While - especially in regards to feelings - I have a kneejerk "no, wait" response to anything that suggests that people's emotional lives and tendencies are determined by gender, Smiler is careful here to discuss the specific pressures guys might feel to conform to certain cultural norms while making it very clear that those stereotypes are not desirable or even truly widespread. And even aside from that, I definitely see the benefit of presenting the book in a way that would make some boys more willing to read it and take it seriously even if they'd be inclined - or have been conditioned - to write off this subject matter as "girly."
Dating and Sex: A Guide for the 21st Century Teen Boy does a great job of presenting information about healthy relationships, sex, consent, puberty, and more in a friendly and fact-based way. Smiler is a therapist and researcher who specializes in male sexual development and relationships, and his extensive knowledge of and experience with his subject are evident throughout. The book focuses on showing boys how to make decisions based on their own values rather than prescribing any particular belief system, making it useful to a wide variety of teens, though obviously parents who want their kids to approach situations from the perspective of a specific religion or other set of beliefs should be ready to supplement this text with more information. (Smiler is inclusive and respectful but doesn't try to explain what any specific religions do or don't consider "okay," as that's outside his area of expertise.)
Even though this is aimed at teens, there were a bunch of important points - especially in the discussions of communication and how to build a healthy relationship - that I was tempted to quote to various adults I know. While many (but not all) teen relationships will be shorter and less serious than adult partnerships, I think it's so, so important that teens get used to good communication and other healthy relationship behaviors from the start, and I thought Smiler did a very good job of walking the reader through how to behave in a mature manner without implying that the relationships themselves had to be super-serious.
Smiler has obviously made an effort here to be inclusive in as many ways as possible, though obviously marketing a book toward "boys" embraces to some extent a gender binary. I was happy to see that the text referenced guys dating girls AND/OR guys throughout, and also discussed a variety of non-binary gender and sexuality labels. The chapter on consent, section on coming out, and emphasis throughout on not using sexist, homophobic, or degrading terminology all helped the book to feel truly modern and useful for both boys who consider themselves "stereotypical boys" by our culture's standards and those who do not.
(Note: The author is a friend and sent me a free copy of the book.)