I've used that and regexbuddy and others over the years. Almost anything the gives you some visual rendering of what's going on is helpful. Personally, I've taken to using the regex stuff in the Jetbrains IDEs, mostly because I'm there already most of the time, and it's 'good enough'. But I'm not always at my own setup, and regexr and similar are always a good tool to have (and to share with others to show them how a regex is working).

If I did this all the time, I might not need tools like this. But complex regex are something I only dive in to a handful of times per year, and it's never the same problem twice.