AFAIK, Haynes only publishes a workshop manual, which probably won't have much of the information found in the owner's manual. For example, your photo of the dash is in the owner's manual, but likely not in the Haynes. But I don't actually have a Spitfire Haynes, so I could be mistaken.
In general, I prefer the factory manuals over the Haynes, but it is just a matter of preference. The Haynes tends to have more diagrams and details for basic procedures, but gloss over some of the more complicated ones; while the factory workshop manual has everything that a professional mechanic needs to know about the car. I'd also say that, in general, the Haynes has more mistakes than the factory manual (but again I don't have the Spitfire Haynes so it might be better than the others).