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Unless I'm doing something stupid (which is entirely possible) or have been very lucky it may not make very much difference which clone you buy (as long as it has a battery and the soldering is ok!).

If my recollection is correct, according to Hugen (who we believe is the developer of this variant of the original 300 MHz NanoVNA) the worst clones not only have no screening but also the manufacturer tried to make up for this by using PCB for the rear panel. Apparently the PCB reflects signals back into the VNA, making things worse rather than better.

I have two NanoVNAs. One came from UK seller sqcase, has 900 MHz 2-trace firmware and no screening. The rear panel is plastic so I called it a semi-bad clone. The second was ordered before Hugen made his available on Alibaba. It came from AliExpress seller Guangyi0016, has 4-trace 900 MHz firmware, does have screening and a plastic rear panel. Both VNAs came with batteries.

In theory the lack of screening of the semi-bad clone should mean more crosstalk between TX and RX channels. I did the following to check:

On both VNAs I terminated ch0 and ch1 with 50 ohm loads and set the display to show ch1 logmag, scanning from 50 kHz to 900 MHz. As the two channels are not connected I believe that any signal appearing on ch1 should consist purely of crosstalk and noise.

Below 300 MHz the signal levels are off the screen on both VNAs (so lower than -70 dB). Surprisingly the unscreened clone has roughly 3 dB less xtalk/noise between 300 and 400 MHz, although it does have spikes at 300 and 600 MHz. (The spikes seem to vary between VNAs. The ICs are being pushed beyond specification so spikes seem to be a matter of luck rather than build quality.) What I'm seeing above 400 MHz is very similar on both VNAs, with displays showing noise that bounces around a lot but at 900 MHz is rarely above -50dB.

I also tried placing a metal sheet behind and then in front of the input/output areas of the unscreened VNA, to see if I could increase the amount of crosstalk. No effect was apparent.

These simple tests seem to suggest that screening may not be as critical as we all thought it was. Could the calibration isolation measurement & subsequent correction be reducing the effect of crosstalk to below the noise floor?

Mike