So, it's been a week since I've had my International-Only BookBub ad for "End of the Line" and thought I'd share some modest results. I'll also include book 2 in the series, "Launch Sequence" (no book 3 yet, working on it!) as I discounted it to $0.99 as well for the run.
"End of the Line"
Amazon - 346
D2D - 69
Kobo - 112
B&N - 0
GPlay - 0
total: 527
"Launch Sequence"
Amazon - 72
D2D - 6
Kobo - 138
B&N - 0
GPlay - 0
total: 216
total for both: 743
Some notes: Google Play did not have either book listed in the BBub markets (UK/AU/CA/IN) because apparently they changed something at some point, and I did not have "currency conversion" turned on. After spending time with BBub and on the phone with Google, Google finally alerted me to where the problem was, but the promo day was already at its end, so... Lesson learned. But it's weird as I've got plenty of sales in UK, Canada, etc from previous years, and I don't remember getting a notice about this currency conversion thing. No big deal, to be honest. The BBub Int'l Only ad was only $160, and I definitely made more than that.
Kobo - did not realize Kobo was going to be this decent. I'm starting to really like Kobo as a platform. Their in-house promotions, scheduled sales/price changes, the dashboard... I really am liking it a lot. Going to definitely put as much effort into Kobo as I do Amazon.
D2D - All but one sale is from Apple, and while Apple has never been a huge platform for me, I'm going to also put some extra effort into it. I really like D2D's dashboard and tools, and again, scheduled sale prices and so forth. Since I don't own any Apple hardware, I'll continue to use D2D.
Barnes & Noble - Not sure if it's just B&N as a platform that completely stinks now, or what. I have done decently well at B&N over the years, but this year has been absolute crap. Not a single sale from this promo, which is weird with BookBub. Must be a sign that B&N is on life support?
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Other notes - Still riding the tailwind from this, and now as readers are finishing the promo book + its sequel, I'm getting a little bit of sales on my other titles. Nothing spectacular, but I didn't really expect it without the BB promo including USA. Had an ENT promo for EotL the day after BBub, so some of those sales are USA-based. Am really hoping for another BBub but with USA this time.
I know that the sales numbers aren't spectacular, but to be honest, I've been out of the loop for a couple of years, and my 30 titles have mostly sat on these retail platforms without a single ounce of promotion. As I'm now getting back into it full-swing, I'm starting to see some lift, and it has encouraged me to keep going.
Facebook - started a Facebook account again (deleted mine the day after the 2016 election as it was just nothing but everyone fighting), and this time I'm ONLY using it for book stuff. Friend helped me by learning the advertising / boost side, and while I've gotten tons of engagements and a decent amount of page likes for my author page, it of course doesn't seem to have resulted in many sales. I didn't expect it to, but as much as I hate FB, I know it's worth having, and will keep trying new things with it (tips would be appreciated!).
One odd thing about the FB stuff is that my friend promoted/boosted the page and my EotL promo with specific targeting of places like individual cities in the UK, Canada, Australia, and India. Almost no engagements or such from UK/CA/AU, but India... tons of likes and engagement stats. Well over 1k+ on multiple posts in terms of likes. However, during this whole promo week, not a single book was sold to an Indian reader across all platforms... Weird, right? Not a surprise, but still, kind of weird. I guess I'm just not destined to be popular in India!
Okay. That's all for the moment. I'm very happy. Could be better, sure, but something something gift horse something, and I'm absolutely not complaining.
So, to reply to the OP's original question, yes, BookBub is still worth it, and as others have said, it's still the #1 gold standard for book promotion for indie authors. Even just an International Only promo.