Here’s a great post by fellow author Nick Stephenson, explaining his experiences with KDP select and an ERederNewsToday promo, with comparisons.
While I agree with Nick as far as it goes, I also think it’s important to point out that ANYTHING that sells your book is good; his well-executed free promo netted him more money than the ENT promo, but the latter was still profitable and put money in his pocket and for a few days expanded his recognition.
I think of things like this as leaping upward for a time, before gravity always brings you down. Even bestselling books eventually fall in the ratings. The only question is how long they stay in that “air.” For the relatively new indie authors like me and Nick, any air is good air.
Combine this advice with everything you already have heard – or should have – about building your brand – website, social media, etc – and you should slowly climb that mountain so that you have more solid ground and less air under your feet.