The caching works. It did improve my performance. But I'm docking the plugin two stars for a couple of reasons.
First, the marketing inside the settings pages is extremely aggressive and quite annoying. This includes an extremely annoying pop-up after you've used the plugin for 30 days that attempts to get you to add a link to your pages or tweet about the plugin or sign up for a mailing list. Or write a review, which is the only reason why I'm doing this one now - I'm hoping to get rid of the box. It pops up every time you touch a setting or do anything in the plugin settings. To me, this is tantamount to malware. Far too aggressive. I appreciate that a lot of work goes into a plugin like this, but this type of aggressive marketing pretty much guarantees that I won't ever buy any of the (overpriced) premium services.
Second, the settings pages are sometimes baffling. As expected with this type of plugin, there are a lot of options. But, again, much of the real estate on the pages seems to be merely an attempt to sell more services, especially on the "Dashboard", which has zero useful information on it. I've disabled "Minify" on the general settings page, but no where on the "minify" page is this mentioned, and everything on that page is still enabled, so unless I'm looking in two different places, I could be changing the settings on the minify page and not know that none of it is going to take effect.
So, it works, but every time I open the settings I get annoyed by aggressive marketing and a confusing and over-designed UI, so three stars.