I really like this extension, it works exactly how I want it to. It would be good to have a slightly easier system to add sites to the block list, but I just copy and paste the example and add my own sites. I'd also like to customise the pop up message. I'm finding it is helping with my productivity and that is great.
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.