ThumbDV and Buster on OS X


I know this isn't the official place to get Buster support per se, but maybe folks here have some clue...

I bought a ThumbDV ages ago (probably a very early rev) and recently got it out to try with Buster on macOS.  
While I can see the serial device appear in /dev when I plug it into my USB port, Buster abjectly refuses to connect to it, saying that it cannot open the serial port.  

I'm using macOS High Sierra.
My Mac is a recent MacBook Pro (consequently I'm using a dongle to present a USB 3 port from the onboard USB-C - but the hardware does seem to be recognized correctly)
I have not installed additional drivers - hence using the default serial driver
I'm logged in as a regular user (though I've also tried launching Buster with sudo - but no difference in behaviour). 

Any clues greatly appreciated!  

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