John Seymour has a lot of fans this side of the water, but to me his stuff is fun to read but not to try and use as a set of instructions. Nearly everything we have ever tried to do from Carla's Emery's book has worked out fine and the one or two that didn't you could tell what went wrong. But John Seymour's "instructions" often leave things out, and he omits entire areas he's not interested in (and couldn't be bothered to research or find someone to do a guest bit on the subject) like most textile work.
I think DH hit it on the head when he said he thought that Seymour's problem was that while he lived in the 20th century, he had learned many of his skills as a very young man from men who had learned their skills in the 19th. So, he had much more of a 19th century mindset than a 20th century one. Therefore he assumed that the average person had a basic pool of knowledge to draw on (he probably thought of it as common sense) that had been lost over the decades between 1910 and 1950.
He was something of a local hero here in Ireland when in his late 80's he got arrested trying to destroy GM crops with his own hands (we don't have them now but that was part of an experiment) and some of his later books that are more history than how to manuals are rather fun and contain great drawings of old farm equipment, what it was for and how to use it now.
But in general, he omits way to many steps for the average newbie small holder to figure something out, unless they have some hands on help from someone who already knows what they are doing.
Carla Emerys on the other hand, mentioned that she had tried nearly major skill in her book at least once, though she has lots of individual recipes and such that she might not have tried herself. Many, like washing laundry by hand, she did not continue to do after she didn't need to, but her instructions will tell you how to do it well, should the need arise. The same with keeping infants warm in a freezing cabin or making cheese on you kitchen table.
Where you really see the difference between the two authors is in animal husbandry, including slaughter and butchering. Carla's information is very step by step and assumes the newbie knows nothing. Take it slow, and you are likely to have a safe and rewarding experience. Before we had her book, we once tried to make sausages from pig innards a la John Seymour and ended up with a complete mess. I forget which step he didn't have listed, but it was another one of those things that are obvious if you've seen this done, but are not if you have no clue.
We have almost all of John Seymour's books, they make fun reading on cold nights, but if the power goes out and I need to make candles fast its Carla I'm reaching for as a guide to making them.