I'm leaving a message here in case someone tries to update an old PRS using PRS+ and the firmware updater.

I was trying to update a PRS-600. The connection to both a Win 10 desktop and a Win 10 laptop was fine, I could use calibre without any problem.

However, when trying to install PRS+ on it, I could simply not get a connection between either desktop or laptop and the app Base flasher by amutin, which suggests that the firmware updater does not work under Win 10.

I dug up an old tablet running Win 7 and sure enough, firmware update without any problem, and so installation of PRS+.

So if you are reading this because you are looking for a thread on PRS+ and Windows 10, you have your answer: use Win 7!