I don't know about the Haynes manual but I know the guy who wrote the other book. John was one of the first in the UK to modify a Vit, I was one of the others and so was that bloke on the front cover, now what was his name? lol.
I have to confess that I haven't read his book yet but he knows his stuff, he writes for a 4x4 mag (4x4 Mart) and runs a Suzuki 4x4 club in Norfolk.
If you're looking for Suzuki books, I can recommend 'Suzuki SJ Gold Portfolio' by Brooklands Books, its a collection of road tests from around the world. They also do one for Track/Kick/Vits, but I haven't seen that one yet.