Tomoson lets you create promotions for your products via their website template. I set up a promotion for my epic fantasy novel Crimson & Cream, asking for book reviews in exchange for a Smashwords coupon code to download the free e-book (JH88U). Tomoson's interface is rather clunky and unintuitive, but once you explore and experiment, it's not too difficult to navigate. I searched Tomoson's database for book reviewers that didn't charge for their reviews (be careful, some do charge) and were interested in reviewing the fantasy genre. I then invited these reviewers (via Tomoson) and activated my promotion.
Tomoson provides statistics on their reviewers, which show their social media reach, their completion percentage for the products the accepted for review, and their rating as posted by the product providers, so you can vet who you want to approve and send a free book to. In addition to the people you invite to review your product, other reviewers on Tomoson can also see your promotion and request your free product. This avenue is where most of my reviewers came from, as few of the people I initially targeted responded.
A total of 25 people requested a free copy of my book in exchange for a review. Sixteen of these people completed and posted their reviews while my 3-week trial period was active. The quality of these reviews spanned both extremes. I received some of my best reviews and my worst review. In total, all but two reviews were positive, and they varied from well-written, polished prose, to quick Instragam blurbs.
Tomoson offers a three-week free trial (which I used), then after that expires, the cheapest option to continue is $99 a month. I didn't come close to an uptick in sales that would justify me spending that much money to continue, especially with only two books to promote. But, the three-week trial period is long enough for you to explore and determine the value for yourself. I imagine an author with a large back catalog could generate a significant amount of reviews in a few months on Tomoson, if that was their goal and within their price range.
The free trail is definitely worth the effort if you want reviews, but unless you are particular in screening your applicants, you may get people who request any and every item they can get for free. My mistake was approving everyone who applied, which came back to bite me with some bad reviews from people who had no interest in reading a fantasy novel. Still, I received 16 reviews on Facebook, Goodreads, individual blogs, Twitter, and Instagram, all for a couple hours work. A final downside is that once my free-trial expired, I can't seem to cancel my account (the only page I can access now is the paid sign-up page), and I keep getting e-mails from Tomoson.
Author Update: I'm continuing to work with my editor on Warlock & Wyrm. We're about 40% through and I'm happy with the improvements, although the process is slow, I feel it is worth it.