It's a nice overview but it glosses over the fact that while the OA database is governed by a CC0 license, the individual address collections in the database are still governed by their own licenses which can be (much) more restrictive. The fact that you can download the data doesn't mean you can use it the way you want. The OA web site hints at this but doesn't address (ah-hah) that underlying problem. That doesn't mean that OA is not valuable - quite the contrary - but I think the fact that it's presented as one big free and open dataset can be misleading.