I've done quite a bit of car work for friends and acquaintances over the years, and I usually bought a Haynes manual for each car I worked on. I've got over 50 of them now..... They are OK for some types of work, getting torque information and such. That said, I've bought an official shop manual for every car I've ever owned personally as they cannot be equaled for the in-depth information. I couldn't justify that for working on other folks cars. I've noticed that the newer Haynes books tend to be more generic than some of the older editions.......
I've got the Helm manual for my Mustang, just wish it was available in book form and not just on a computer....