I eventually ended up with two.

Both simply have a usb plug one side and midi out and in the other side and both cost about a fiver (UK)

I found one that specifically mentioned Linux so I ordered it. After ordering I noticed it was coming from Hong Kong and would take some time, though it was despatched promptly enough. In the meantime I found one on Amazon. Although the spec only mentioned Windows and Mac, two of the customer reviews said theirs had worked on Linux so I ordered one and it came in just a few days and it works a treat with my Linux Mint set up. I use the default audio set up of Alsa/Pulse Audio with no problems. I got a 3.5mm Y connector from Maplins so the audio output from the synth and my computer are both connected to my external speakers and that works fine as well.

The one from Hong Kong arrived eventually. I've not tried it, but will keep it in case the other one gives up.

It's nice to have my Yamaha synth module working again as I did quite a few arrangements of tunes using Noteworthy and I can play back and record the accompaniment part and record myself playing the melody. Works pretty well.