I had been looking for a VNA which would work outdoors and which could optionally be connected to a PC with software for bench work indoors. The VNA is built in a nice metal box with N connector sockets. The label on the back says 50k-3GHz, H/W version V2_2.

It came in a nice protective case & included a calibration kit.
I loaded the VNA-QT software onto my Ubuntu Linux PC. This allowed me to upgrade the firmware on the VNA.
Updating the firmware
The VNA had version 202001117 on it when it arrived. This seemed to be a bit buggy, so I looked for the latest version. I found Unofficial Hardware Variants , “V2.74” from blackmagic 2020-10-13 firmware download worked OK. 106kB loaded.
Holding down the left-arrow button on the VNA (the button closest to PORT1) and switching on the VNA gave me a white, blank screen, indicating serial upgrade mode.
SAA2/NanoVNA V2/V2 Plus/V2 Plus4 user group forum
I have discovered today (2-April-2021) that the original developers have a dispute with Hugen/Zeenko. So having found what I took to be officially-supplied firmware for “Unofficial Hardware Variants”, I now see there may be really no support at all. This is a complicated world!