Since January 1st, I have place three book into KDP Select to assess its viability. I launched Rigel Kentaurus into KDP Select first. A while later, I unpublished both my collection Accretion, and my first novel Neanderthal Swan Song from everywhere but Amazon.
My first free days on Rigel Kentaurus went very well, and I managed to sell about 140 copies. A month later, rumor was that Amazon changed some of their algorithms and what had been known as the 3-day bump, a sales surge three days after coming off a free promotion, all but vanished.
Rigel Kentaurus sales have dropped ever since. Neanderthal Swan Song did not see enough of an increase in sales to say KDP Select had any influence. Accretion never sold a copy at all.
Amazon changing the algorithms is changing the rules of the game after it starts, and if I can’t get out of the three month contract when they change the rules, I question whether they are in breach of contract themselves.
In its current state, in my opinion, KDP Select is no longer worth participating in. The exclusivity is a killer. I had made sales through Smashwords and lost my ranking on many sites when I unpublished. I did not see enough sales at Amazon to justify removing it from other venues.
My “borrows” always numbered in the single digits, with sales far outpacing them.
Right now, I do not see any advantage whatsoever in using KDP Select under the current algorithm. I do not plan to participate in the future unless things change in favor of the author.