The answer you'll get here is 'why would you give your work away for free?'
Unless you have a series of books, and you want to give the first one away as a teaser to entice the readers back, what's the point? Once they've got your book, they're not coming back, are they? And so many free books never get read, so the story goes.
If you've got multiple books out, even if not in a series, you might see a small (short-lived) gain in sales of other books, but other than that, the general consensus would probably be, don't do it.
Anyone use this? Can you say if it interests readers in the total output of an author? Does it lead to purchases, reviews or recommendations? Any specific advice? Thanks.
Yes, no, no, no, no, and no.
Search the forums; there are hundreds of discussions on free promotions. The bottom line: unless you have a large back catalog or are promoting the first book in a long series, it's a waste of time. Free books are rarely read.