I was looking for a Aperture 3 plug-in, but I see that most of them are old. I was looking for a good one to add post depth of field but seen one from 2010. Seems outdated.
Not all plug-ins are listed on the Plug-in page, and some of the listed ones are no longer available. That page needs updating.
Before you download and buy any plug-in, check the compatibility with your Aperture version. Some plug-ins may not work with Aperture 3.4 or later, see:
Aperture 3.4 and later: Some third-party plug-ins are no longer compatible
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