Thank you for pointing out that device.
I believe you are correct. I was only able to find a listing on Amazon for a used one of the M3K devices. Also found a listing on ebay.
I need a device with Bluetooth as my car doesn't have an auxiliary jack. Suppose that I could also make use of an low power FM transmitter also.
The thought process for the purchase was that I wanted a standalone DAP without a touchscreen (iPod-esque), without wireless connectivity, with expandable storage, and not running Android. The M3K also has good Rockbox support including dual-boot, so I swap between that and the native Linux firmware at times.
I am considering getting a second device of some kind with Bluetooth because there are occasional but persistent times where it honestly would be nice. Ideally it'd still be running a pretty basic OS, though.