[ankimal]

They make scraping as easy as finding the right jquery selectors (once you inject jQuery onto the page) but can be very slow as compared to a vanilla HTML only scraper.

In my experience, a phantom/casper implementation could take upwards of 5-10 secs. to process a single page (almost 5-10x slower). This, even if you disable load of remote images and plugins.

[zenocon]

There is a startup penalty to getting phantomjs executable up (including all of its WebKit internals), but once you're there, I've never had any performance issues. Roll a script using casper.each() and feed it an array of urls. It is typically very fast for me. You can trap on the page loaded event and do some benchmarking, but I would disagree with your premise that using PhantomJS/CasperJS is slow.