It works reliably 95% of the time and blocks things when I inadvertently get distracted. The other 5% of the time, it closes useful tabs, but tweaking the prompt helps there. I hope it learns my browsing style over time and gets better.
I have been using Locked In for a month now, enables me clearly define what I intend to work on and actually helps me in sticking to it. Also the insights dashboard is a sweet touch.
It's a tool that I didn't knew I needed!