Buyer beware, this plugin creates a "temporary" user with no email address for every visitor to your site (logged in or not.) It's supposed to clean up after itself, but doesn't. The end result can bring your site to its knees.
When our site hit 20K fake users, arriving multiple times a second, we started having twice-daily crashes, page response times north of 10 seconds, etc.
Don't take my word for it, read it in the developer's own words.