Hi Philip,
Apologies for the delay in responding.
The Linux version hadn't been updated for a while so I'd removed the link from the downloads page. I've since updated it to the most recent version but forgot to add the link back - I'll add it back to the downloads page when I get a moment.
You are correct in thinking you need to choose a ttyS## name that does not already exist. I'm not sure why the link would go away after reboot, but shouldn't matter.
As the serial ports are owned by the root user and the dialout group, you will either need to add yourself to the "dialout" group (best option) or run the config utility as root (best to avoid running things as root). Otherwise the config utility will not have permission to access the serial port and so will likely hang.
To add yourself to the dialout group, you would run the command below, replacing <username> with your Linux user name.
sudo adduser <username> dialout
I realise that info is missing from the readme, so I will update the readme with the extra info.
If that doesn't solve the issue, let me know and I will investigate further.
Kind Regards,
Tom.