Now over 40,000 impressions (or whatever the proper word is) and just 7 clicks, at a cost of $8 something. Quite a low percentage, but not zero, so structured and targeted better this may be a worthwhile thing to do again.
Most importantly one click has to take people directly to the book, not as with this, to my Facebook page where they have to click again to go to smashwords etc.
But some exposure, and more importantly an idea of how this all works.
Over $1 per click would be worth it perhaps, if they actually downloaded the book.