My experience writing a review on one of these sites is getting it repeatedly sent back by the admin to reword it to better fit their content requirements. Meaning I can't say what I want to say, and having a limited character count, so I can't say all that I want to say.
Reading other reviews, you see a pattern forming. Total waste of time. What I'm reading is what the site admin wants me to read, not what the reviewer wants me to write.
Would rather be subjected to ads and say what I want with minimal admin intrusion.