I get your point, but since the javascript is his copyright, it’s his right to do so. But I agree it is not very customer friendly. Many people here develop sites for clients and a monthly or yearly fee is out of the question in such a case. A one time fee would be preferable there.
The thing I really don’t like, though, is that it isn’t mentioned anywhere that this plugin is ad supported. Not in the main description, nor in the FAQ. Even on the Printfriendly website it isn’t made very clear. You have to notice the small text link saying Ad Free Version to get to that part. This is a clear case of tricking you into installing the plugin, than finding out about the ads and thus tricking you into taking the subscription.
Of course, since the plugin is published under the GNU public licence, I’ve checked the code to see if the ads could be removed. However, the essential javascript code used by the plugin and hosted on one of the authors servers is not published under the GNU license, but is copyrighted. And guess where the AdSense code is included…
I’m also a little disappointed that a highly respected plugin developer like Yoast is involved in this.
I’ve just discovered another plugin, that looks just as good as this one (or even a little better) and I haven’t discovered any ads there yet. So I will be going with that one and leave this one alone.