Simple to use, works exactly as advertised, very effective, no clutter.

Excellent! Does exactly what is says.
Perfect for sophisticated URL blocking.

Exactly what I am looking for!

As simple as possible. Well, as long as you know regular expressions.

Good

URL blocking by using regular expressions - the best way! Best blocking plugin for Firefox Quantum

Wow this is exactly what I was finding for...

Best website blocker that I could find. Great job allowing for regex and super simple and easy to use. Love it! :)

Blocking sites based on regexps is powerful and works well with this extension. Unfortunately it's not possible to add exceptions to a blacklist, but it can be done by negative lookahead.
I second the password protection request. Thanks.

This is the most awesome productivity application out there.
Just a suggestion though, please add password protection, or at least some measure by which user might not get into the add on options, remove the keyword of the website that he wants to access and access the website. This kind of defeats the purpose.