This is an update based on experiences in Nov 2019 installing on a Mac book with Parallels desktop version 15 and Qest4 Bluetooth.
1) Parallels website makes it very simple to get Windows 10 installed after buying Parallels software. We chose the Home version of Parallels for $80 lifetime rather than the business versions payable per annum. Licensing of Windows happens when you choose to via MS website.
2) Once Windows is installed, before installing Qest4, it is good to allow Windows to do all updates. Not doing so resulted in a mysterious loos of the Bluetooth drivers, and need to reinstall device.
3) The default view in Parallels version 15 is 'Coherence' mode which shows the Windows taskbar at the bottom of the Mac Screen and Windows Apps within the Mac screen. It's a very fluent experience, but initially confusing for Windows and Mac users alike.
4) Before the device will connect it is necessary to access the Parallels menu via its Mac taskbar icon and configure the devices section for Bluetooth Sharing with Windows.
5) Windows Bluetooth pairing must be done as usual. The device manager will show 2 Bluetooth serial ports under Ports once device has successfully connected.
6) We experienced 2 instances of needing to re-install the device (delete Bluetooth Device in Windows, reboot Windows and Add Bluetooth device afresh). One time was due to Windows update, we think. The second time seemed to be just triggered by Windows being held in Suspend Mode when Mac OS was shut down. (Mac OS shutdown does not result in Windows restart).
7) Due to 6 we found that the safest strategy for continued use of the system was to shut down Windows after finishing with Qest4 and then close the Macbook or Shut it down.