I spent the week-time trying it. I did install it on a USB drive. I started from a Carbon Copy Cloned version of my main OS that I updated. I had to give up, I tried to update a project I am working on and after a 1-hour git pull would not finish even if there were only a few files to update. Everything takes forever even if the CPU is almost idle, I suppose trying it on an external USB drive is a big issue even if I did that in the past with other macOS versions...