The mass-market paperback is smaller and therefore has more pages. The paperback version is the one with the foil laid into the cover art and, to my mind, is the more presentable version. There’s a difference in price of course – £8.99 for the paperback against £4.62 for the more compact format.
On Amazon it’s easy to confuse the two so make sure you know what you’re paying for and that you get the version you prefer.
For US readers, mass-market paperback is the only physical version of Black Feathers on sale.
However, the book is also available in CD, audio download, and is a DRM free e-book if you purchase from The Robot Trading Company
Happy reading, whatever you choose…