I am a customer of Atom.com and Afternic. My feeling is that Atom does a good job of helping people discover branding opportunities with listed domain names, and Afternic does a good job of helping domain name buyers purchase the domain names they are looking to buy.
At the moment, I have just shy of 250 domain names listed via Atom and I have more than 2,000 listed for sale on Afternic. All of my Atom-listed domain names are also listed for sale on Afternic, but there are rules I am required to follow in order to do so. Since I always list my domain names on Atom with “coins,” the primary rule that I am required to follow is a 10% markup on the BIN price at Afternic.