For those interested in the value of the free train, here are the results of my free month.
In September (before free) I sold 35 books total on Amazon US (and some unknown small number on other sites where I can't view sales immediately).
In October (and the last day of September post-free) I gave away 14885 copies of Stray on Amazon US. Many of these will have been to people who will never read the book, or who are not the ideal audience for my genre, but just sensibly collecting the freebies while they're there.
However, some obviously read the book, since I sold at Amazon US:
- 638 copies of Lab Rat One
- 48 copies of the Medair duology
- 36 copies of Champion of the Rose
- 12 copies of The Silence of Medair
- 11 copies of Stained Glass Monsters
- 9 copies of Voice of the Lost
Stray also went free on various other sites and (though I can't say exactly how many), I seem to have sold a few books on those as well. I also picked up over 20 reviews on Amazon, and maybe a dozen reviews on other sales sites, book blogs, Goodreads, etc. Reviews are valuable, both in explaining the book to potential readers and by sheer weight of numbers showing that the book has been considered worth reading. I'd read that the free train does attract negative reviews and found this to be true - I picked up two more one star reviews (from people reading only the opening of the book), but this was more than balanced out by positive reviews.
The free train is a way to raise a book's profile, and get into Amazon's Also Bought recommendations. I'm fairly sure that Stray will sell at least a few a week despite no longer being free. It remains to be seen whether word of mouth will lift the series' sales again, but overall I would unequivocably recommend the free train - at least for the first book in a series.