Do you play nice with Amazon's Terms of Service?

Yes. According to Amazon’s Community Guidelines,

authors and publishers may continue to provide free or discounted copies of their books to readers, as long as the author or publisher does not require a review in exchange or attempt to influence the review.

On BookSirens, readers are NOT compensated, incentivized, nor required to leave a review. They are also NOT influenced to leave a biased review. Readers simply use BookSirens to discover complimentary review copies and leave honest, voluntary reviews.