Ask any up and coming developer what they would like to do in the next year or so and you'll invariably hear, I'd like to become a Development Team Leader Hopefully most will have actually considered the change of role and be looking for new challenges and ways to contribute more to their chosen pro...
Here's my experience TL:DR; take: requires learning how to manage people, delegate. You'll spend 80% of your time in pointless meetings and writing docs. Moving between jobs will be harder because companies are most likely to promote their seniors to TL instead of hiring and also because salary expectations are higher.
Fadell worked in the R&D department of various companies you may have heard of such as Apple, Google, Sony, Philips, Motorola, Toshiba... as well as others you likely haven't heard of (because they were moonshots that explode mid flight - one tried to invent an iPhone in 1990 when touch screens were shit, networking was wired, and batteries were disposable. Talk about ahead of it's time). That failure wasn't wasted - a lot of the mistakes they made were avoided years later when he was leading one of the teams that invented the iPhone (not from scratch, but by learning from past work).
He's now basically retired and spends his time advising the next generation, but that book covers all the basics. It really is a gift to the billions of people who can't ask an experienced product developer for advice. And if you are lucky enough to be able to ask, the book will give you enough knowledge to avoid asking stupid questions.
Thanks to my experience, and other lead devs leaving the project, I'm sort of "pushed" in this role. I'm not sure if I like it or not. Sure they see value in what I can do, but it's also more responsibilities and more meetings. I always liked it to go with the flow previously :D
In over 20 years, I have never wanted to be a team or project leader. To me, that requires a very different set of talents - management and people skills first and foremost.