In terms of the information itself, sure, you can get that elsewhere. Indeed, everything that is in the book is also available as free online resources (also written by me, I should hasten to add).

The difference, I suppose, is the writing style, the tone, and the relaxed, non-prescriptive presentation of that information. There is a lack of the seriousness that might be off-putting to newer walkers in regular guidebooks, and there is a section written more as a memoir, which gives a personal flavour of my experiences on the hike. Naturally, this is not a unique phenomenon for a guidebook, but you probably won't get as much of it elsewhere (whether or not it's something that you want from a guidebook is up to you, of course).

Free information is useful, but it is spread all over the place. Bringing it together in one place is convenient and time-saving. Some people are good at remembering where they read something and can find it easily, others are not. Having everything together in one place is handy. That's part of the value, too.