ZTE Valet smart phone on USB looks like CDFS file system (read only, write once). Windows Explorer only shows the USB driver which is installed on first use.
The ZTE phone file system has multiple partitions. You have to manually select an access mode by clicking a button in Settings/Connect to PC. The four modes are: Charge only; Media device (MTP); Camera (PTP); Install driver. I was in the Install mode (default for first time connecting to USB port), so Windows Explorer showed only the Install partition. After selecting the Media mode, Windows Explorer shows the Phone and SDcard partitions. The ZTE "USB driver" is a program installed in C:/Program Files (x86). The two ZTE "Assistant apps" are a web link to http://joinme.ztedevice.com and an uninstall program.