A fellow maker put the diff probe under test, with some serious equipment: https://electronicprojectsforfun.wordpress.com/a-100mhz-differential-probe-from-hackaday-with-keysight-autoprobe-connectivity/

We are now working on a slight change to the offset current injection that won't impact CMRR as much, and an enclosure.

The design that was posted previously (with +/- 2V5 dual supply) requires voltage regulators that are pretty specific, expensive and hard to get, so we're looking into building our own from TL431 references, TLV911 OpAmps, and a pair of FETs. Here's the positive rail:

These parts are comparatively cheap, and replacements should be easy to find. The simulation results are looking promising, and we'll just test it.

A simple dual output DCDC converter can be used to generate the required +/- 5V from a scope's USB output - at least for one probe. Or two, if the DCDC can supply enough current.