The piano specialist at my local sheet music store informs me this is currently the best-selling piano method for adults. It's not hard to see why.
I had a student who was going through Bastien's adult method, slogging along. I switched him to this one, and he started making sparkling progress. After a few weeks, I asked him what he was doing differently. He told me he just loved this book.
As a teacher, I can tell you this book doesn't go as deep as the Alfred's. It's only two books, whereas not only is the Alfred's three, but goes a lot deeper with the student before pronouncing him finished. At the end of book 3 of Alfred's, for example, the author proposes you play Fur Elise and Toccata in D Minor in their original forms. There's no way you're going to be able to do that after merely going through the 2 Faber books.
But I would say this book does have an advantage over the Alfred's: it chips away at your piano ignorance, so to speak. Every lesson is short and gradually incremental. There are no monsters in the book to stare down a student and discourage him. No, songs look easy to play and you get the feeling of making swift progress without as much intimidation.