I read this book years ago and got a good deal out of it. It is not as detailed as Sloane's other books that tend to deal in detail with making single instruments, but, for someone who has made other instruments, this shouldn't be too much of a problem. I bought the book because of the rather more detailed instructions it has for making banjo and drum shells out of strips of veneer. On the other hand, for anyone wanting to make a banjo with no prior experience in lutherie, I think the overall instructions might be rather sketchy.
Sloane does give perfectly good instructions for making regimental drums, tambourines and (flat topped) mountain dulcimers, and reasonable instructions for building a Hardanger fiddle (but I know of no other book that has instructions for one of those).
The book claims to show how to make an alto recorder, but, in reality, it just shows the dimensions and gives little more than a photo essay on how the process is completed in the Dolmetsch studios -- interesting but of little use to someone without all the specialised tools. I know, from personal experience, that cutting the fipple end (for example) is a far from trivial job.