The plugin is free (Xbench customers do not pay anything extra for it), but it has as requirement Xbench 3.0, which is a subscription-based application that can be ordered here: http://www.xbench.net/index.php/store/order-xbench
This is pretty similar to the Grammar Checker plugin in the SDL Open Exchange, which is also free but has as requirement that you have a Microsoft Word license, which is not free.
During the Xbench trial (for which you signed up on March 9, 2015), several notifications were sent via email as you progressed through the trial.
Perhaps you missed those notifications or they ended up in your spam folder.
Your Xbench trial lasted so long (almost a year) because our 30-day trial is for 30 days of actual use, not 30 calendar days, so that users can evaluate it at their own pace.