When I played around with it using Linux, I had probably damaged the partition. The device reported ``full'' even when I just uploaded 70MB of music. Reformatting it using the supplied utility software fixed the problem, but that did not inspire confidence.
I was later informed that the mtools package works fine with the BP300. Sure enough, mcopy, mdel worked with the device without any trouble. You need to include the necessary USB related options (either compiled into the kernel or as modules), and you need to add a line to /etc/mtools.conf as follows:
drive f: file="/dev/sda1"
Of course, you may need to change the drive letter sdb1 and etc. if you have other SCSI or emulated SCSI drives.