My overview take is that KDP Select is good for new authors with a little bit of a funnel but once you get more known, you want to give your book value by not giving them away free.
I think there is a threshold where you can only give away so many books before it doesn't justify the means.
Here is what I've found ~ with some promotion, a little hype with twitter we were able to get one under 10,000 downloads with one title and we so far have gotten an extra 13 reviews (so far) from the effort.
I don't think KDP Free is what it was, and it may continue to decline, but doing free in a smart way is still the way to attract new readers to you. I still do a free promotion, but in other forums.
ACTION ITEM: Try FREE in places like Facebook, Twitter, blogs and Kindle.
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Troll River Publications
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