The add-ons does the job of blocking websites that will steal time through procrastination. However, it could be a little easier to use as websites have to be entered with specific coding e.g. *://*.facebook.com/* but a fairly easy work around is by adding a new line, pasting the above example and replacing the website address inside the special characters. Once the website has timed out, there isn't a prompt saying that your time has expired, it will just reload an empty new tab (unlike leachblock which will display a message), so it's easy for a novice to mistake this for an error. Other than that, can't complain.