I've been active on a thread in Goodreads, Best Bang for the Buck Book Promos; I've reported my results there, so it seems only proper to do so here too.
I've had two promos through ENT, both successful. Both were of books priced at 99¢ and I showed at least a small profit at the end of the day. The most recent promo garnered more than 100 downloads.
Second best has been Book Sends; I've had one promo, one attempt declined, a second scheduled soon. Same conditions, 99¢ discounted price.
Third is Free Kindle Books and Tips. I moved some 46 books but didn't make the cost back; net loss, about $7, allowing as much credit for the promo as possible.
Fourth has been Fussy Librarian; I lost about the same amount, mainly because the cost of the promo was $16. Partially successful.
I keep careful records, recording sales by book right up to the moment the email goes out. I corresponded with one promoter and his clickthrough count was exactly the same as my calculation, so I'm confident in my results.
No other site has produced much in the way of results. One, Kindle Book Review, was a total bust, despite the $40 promo fee. Best advice, avoid this site like the plague. I asked the site owner how many subscribers he had in my genre (SciFi), but got no reply.
Most of the sites are quite small as yet; many seem to be less than a year old. Fussy claims about 80 000 subscribers in my genre, but if so, they're not buyers. Maybe they only download free books, which I prefer not to do.
For most of the smaller sites, I rate them as 'not yet'. Maybe, in a year or two. I haven't tried BookBub (wow! that FEE!) or Book Gorilla. I don't expect to do business with BG; they sandwich Indie books between former bestsellers from the NY Times list. Tough to compete with those authors if you're as new as I am, not quite a year publishing my books.
