I've always been interested in niche selling. It makes sense, as it is a much more targeted sell, where larger competitors may be absent, under represented, and are likely lacking in terms of the service offered to the target audience.
Own your own niche, covers a lot of the basics in addressing a niche market, and makes for an easy read.
Even though your niche doesn't have to be online based, if the niche is specific enough, it likely will be, in order to gain a larger customer base. This likely explains the book's emphasis in online strategies.
Thus said, it is a well structured book, that will make a nice addition to your library, and help you in covering all your bases in addressing a niche market. As you business develops, if you feel the need, you may be interested in additional books in any of the specific topics covered.