For the benefit of people who skim-read &/or don't look at the faq tab, perhaps you could add a word like 'paid' to that phrase to clarify that the API key needs to be purchased? It might prevent more topics like this one being started, however I wouldn't bank on it.
@cubecolour - FAQ are usually reserved for operational nicites and would be an acceptable place for the developers to attempt their upsell.
I did an analysis of the Features page, and according to my word count (based on total paragraphs devoted to a feature), 77.8% of the Features page was devoted to a discussion about the usefulness of the API key. Even for careful readers, it is easy to overlook the purchase requirement.
The copy I referred to is on the front page of the project description.
At some point the user is responsible for reading the copy about any plugin they download, not just this one.
@wpmudev - Please see my note about about the focus of the written copy of the Features page. A reasonable analysis of the copy comes up with over three-fourths (77.8%) of the text being a sales pitch devoted to the API.
Your "At some point" comment works both ways. Sellers are even more liable under the requirements set forth by the FTC.
Users are inundated with promotional advertising, and slipping in a single statement about there being an additional cost is not enough. According to the FTC regs, the disclosure must be noticeable and obvious on the "sales" page, which is certainly what the Features page has become.
I do like WpmuDev plugins, and although I find some of them to be clunky to use, they solve problems that are not readily available from other sources, and they are updated for each new version of WordPress, which is no small feat in and of itself.. I will continue to selectively use them, unless I am banned because I complained, on a going forward basis.
Because I had used Anti-Splog before, and was familiar with its operations, I got excited when I saw it available in what was originally a repository for free plugins. I felt blindsided when I came to the API purchase requirement in order to get the features that were so described on the Features page.
If I had been totally wrong, I would have slunk away in silence. But, with the amount of text devoted to the API, I didn't see where I was mistaken. I still don't.