Usually, forums are used to discuss solutions for issues and problems. I would like to use the forum to give positive feed back.
Yesterday, I used the new UBPorts Installer to install Ubuntu Touch on a used OnePlus One smartphone that was running on Android. The user experience of UBPorts installer was excellent !!!
The installation process took only about 15 minutes and required minimum user interaction and there was no need to look at any documentation. The developers have also thought of nice details such as a brief visual guide how to set a OnePlus One device to fastboot mode. Installation was absolutely smooth.
[Following is solved now, see comment by rocky58: Only after the installation was complete, I run into a few problems, but this had nothing to do with the UBPorts installer: My OnePlus One was not recognized as MTP device, so I couldn't easily copy my old contacts and SMS over to the new device (https://github.com/ubports/ubuntu-touch/issues/13).]