I used to use BookSirens. I no longer do for some very good reasons.
Yes, reviews are important. However, what you want are reviews from fans. The reviews you get from these services tend to be fairly mediocre, in my opinion. The people attracted to these sites are getting their free books without being either invested in the author or the story.
I suspect that any service that requires your participation in reviews is going to be gamed by people leaving a bunch of reviews in short succession, just so they can get their book on the site. That doesn't encourage someone taking quality time to sit down and read your book. Plus, I'm not sure a site of authors reviewing authors is a really good idea.
