That's how USB sharing function on the router works...
Why do you have to access it via Network Neighbourhood?

What is the purpose of the Network Neighbourhood access technique if it does not allow reading and writing of files on the flash disk?
Eventually, I want computers (and televisions) on the network to play movies on the flash disk and they don't use FTP to access files.

I want computers (and televisions) on the network to play movies on the flash disk and they don't use FTP to access files.
Media server?
http://www.tp-link.com/en/faq-731.html

Thanks for the link. This morning I discovered that Windows Media Player can play pictures, videos, etc. on the flash disk, so that puts my mind to rest about some things. However, I want to use the flash disk for backup and store binary files, etc. that will be useful throughout my network... i.e. not just pictures and videos. Sooo, I want to mount the flash disk as a Windows 10 disk usable for read/write throughout the network for any purpose.... can you tell me how to do that?

However, I want to use the flash disk for backup and store binary files, etc.

Cannot do that. Storage Sharing/FTP Server/Media Server/Printer Server are what USB sharing supports.

Other TP-Link documentation:
"Choosing “share selected folders” will open up the Sharing Content (Media file, Document files, Compress files and so on.) below to allow you to configure the folders you would like to share, the write access, select guest accessibility, enable authentication requirement for accessing the selected folders, rename the share name, and select your volume name. Once you have selected the sharing method please ensure you have clicked save."
indicates that I can store documents and general files, rather than just pictures/video on the USB disk. So, if you are right, I want my money back... deceptive advertising.

If Share Selected Folders is selected, only the folders you specified will be shared. Youhave to click the Create Share Folder appeared to specify folders allowed to be shared. That's what it means, isn't it?
Is it what you need?

Using Windows Media Player I can play videos/pictures on either the whole USB disk or selected folders, if I made such a restriction. I have absolutely no complaint with videos/pictures. However, documents are invisible to Windows 10. In other words, the current software allows the router to read videos/pictures, it seems and everything else is ignored. So far, I have not tried to write files to the disk when it is plugged into the router. So, I cannot use the USB disk for network backup or to upload movies/pictures from network computers... this is a major disappointment for me. However, once I get one of the newer TVs, at least I will be able to play movies on the USB disk, I think, to the TV. So, the capability of the router is 1/2 i.e. one out of two enhancements that I hoped to provide to my home. It is amazing to me that the USB capability is so limited.

Hi Ashton,

I have a C9 but I think it would be the same as with the C8 you have. I did not select to share a specific folder but rather share everything. Now, with this, the default setup, the router shares files as follows (assuming your router's IP is 192.168.0.1):
- Via FTP: ftp://192.168.0.1:21
- As a samba share: smb://192.168.0.1
- Through upnp using the router's mini DLNA server.

With this now I do the following:
- I have a media player (android TV box running Kodi) that can read media files from any of these share options (smb and ftp being the best).
- I have mapped on my Windows 8.1 PC a network folder at \\192.168.0.1

With the network folder I can copy anything I like over to the disk (i.e.not only media files). Isn't this what you are looking for?