As they made big claims about CMRR, it was the first item I tested.
Right off the bat, I found one of the two probes to meet CMRR spec, while the other one was off by a bit. Slightly disappointed, but hey, you are supposed to be able to tune the CMRR spec, right?
Tuning the CMRR performance requires their dodgy no-name software from their equally dodgy website, and the software was windows only while I run Linux on my machine. So I ran the software within a VM, and it worked fine.
The manual actually does not contain the instructions for tuning the probe, but I found a PPT on their website that does describe the process of tuning the probe.
The software talks to the probe through UART, and there are 4 sliders for each of the x50/x500 ranges. One is for offset, one for low frequency CMRR, and two for high frequency CMRR.
The described process does not require any special equipment other than a scope and a SMPS.
1. Short the inputs and adjust the offset
2. Connect both input to mains live wire

and adjust LF CMRR until you don't see the signal
3. Connect both inputs to the Drain of a square wave-ish driven, hard switched SMPS MOSFET

, adjust the HF slider so that the signal is minimised. The bottom right slider is to reduce the spurs on the probe output caused by the switching edge, the top right slider is then tuned so that the top and bottom edge of the switching waveform lines up to be perfectly flat.
I used method 1 and 2 to satisfaction, but method 3 was a bit inconsistent (and too dodgy) for my taste.
I tried hooking both inputs to the center pin of a function gen outputting a fast switching 10V p-p 1MHz square wave and tune it that way. I do see the signal change as I adjust the sliders, but for the bottom right slider where you are supposed to minimise the switching edge residual, it was hard to determine if one ringing response was better than the other. As my goal is to try and match the two probes I have (rather than trying to hit certain performance numbers), I ended up using my scope's bode plot function, and adjust the sliders until both probes matched.