So far - All the Yamaha arrangers that record MP3 to USB stick have a bug that stops the recording saying the device is busy.
This feature does work on several brands of USB stick, but those specific ones known to work are now becoming hard to find.

Anyone want to bet this feature now implemented on the new T5 will still have the same bug?

This never happens on my Pa900 and I have tried every USB stick I own.

Bill G