I was subscribed to the single-book option box for two months and liked it fine!
The books came brand new, autographed, were each over 4-stars on GoodReads, and the shipping was prompt! The books I received were cute enough and weren't amazing by any means, but they sure were fun to read!
In the end, I was disappointed that the single-book box doesn't get any extra swag or fun extras at all, which I was looking forward to. Just a book. $16+ (including shipping) per month for a single autographed paperback and nothing else ended up being a little much for me... I think the value is probably better if you get one of the larger box options.
I love getting Knit-Wise yarns every month! You get two good sized skeins for a good price, and they're usually a blend of natural fibers and acrylic. It's been great to slowly add some surprise project yarns to my stash, and getting more than one skein of the same kind/color every delivery is really thoughtful. I wish they would put some more information on the label (yardage is missing entirely!), but at the end of the day, it's a really great subscription!