Hi Jason,
I hope I can clear up a couple of your questions about Moz Local (I am its product architect).
Why aggregators (like Localeze) are important:
I wholeheartedly agree that claiming still makes sense for sites that are bringing you serious traffic where you really want to fine-tune your profile. However, this should be balanced with the time it takes to maintain a presence on each of these sites. As Mike Blumenthal says, "you claim it, you own it," and if anything ever changes with the business it'll need to be updated on all the sites you originally claimed.
Listing properly with aggregators is the best way to ensure maximum coverage for accurate listings across dozens and hundreds of sites that you will likely never have time to claim listings on. Additionally they maintain relationships with some sites (such as Twitter, Apple, TomTom, and other GPS companies) that don't even have a public-facing portal through which to submit information.
# of clients:
Each location you submit through Moz Local costs $49/year. You are able to submit multiple clients/locations using the same CSV spreadsheet, and manage them all in a single account.
Duplicates:
We have built a fairly intricate location clustering algorithm (likely not as robust, but conceptually similar to Google's) which ties each listing that you upload with close-match listings on the sites in our network. Only if we're not able to find any close-match listings do we create new ones.
Within your dashboard, we then show you all additional listings which still appear as close matches, and give you direct ability to individually close these on sites in our network. Soon we'll have a button within the dashboard that will allow you to close them on the sites in our network with one click.
What happens on cancellation:
Unfortunately this is up to the policy of each of the sites in our network. In the case of all but Acxiom and Localeze, we simply stop pushing information when you cancel. Acxiom and Localeze, however, will revert your listings back to their original status once we tell them that listings are no longer being managed.
Hope that helps!
Best regards,
David