Anything in particular that makes you like them so much?
Part of it is me coming from Afternic , which is virtually impossible to sell at right now using Make Offer, so any port in a storm, right?
But even so, Atom is top-notch in my opinion. The landers are fast, the support group is excellent, analytics are top-notch, the offer/negotiation area is fully-featured, I'm getting inquiries and sales, payments are quick and smooth - I'm just very impressed. And knock and on wood, as the last time I was pleased with a domain marketplace GD bought it, then closed it down.
* I don't mean to paint Atom some magic solution, as it clearly isn't, but it does give you the tools you need to succeed. On Afternic I was getting consistent offers but the brokers would just sit on them and send out "Are you still interested?" emails every week or so. So I made zero sales in Jan-Feb and I had pages of "Stalls". With Atom, I have regained full control over the negotiations so I am now translating some inquiries into sales, which is near-impossible (unless you use BINs and take the brokers out of the equation) to do at Afternic.
So if you're using Make Offer and coming from Afternic, and you liked Dan, you're going to love Atom. If you're already sending traffic to places with self-brokerage and negotiation like Saw, Dynadot, DomainEasy, etc., or using your own landers, then it's not going to be such a big change.