I have thought about Tripadvisor as being all about reviews. i didn't realize you list vacation rentals by owner, but it would be a great idea, if the reviews were accessible. I am looking for a place in Paris for 4 days in September, and will probably go with HomeAway or Air BNB instead because those sites have reviews of the property/owner/customer experience. I just don't know what to make of some place with only one review, written 10 months ago, or the many places that have no reviews at all.
Your assistance with secure payment seems like a benefit, and perhaps safer and more convenient than HomeAway and AirBNB, except no reviews to hear from others how well it really worked for them in the event of not being able to stay in the room they expected, and having to make alternate plans immediately.