Today, I performed a quick check of a network analyzer without using a BNC adapter (with differential input). The circuit under test was a simple RC low-pass filter, with a cut-off of around 294 Hz. Here is a schematic with indicated connections for Analog Discovery 3:
Here are the results of measurements:
Measured -3 dB was around 318 Hz and was really accurate if including the tolerance of the capacitor. The used resistor was 1% precision. Bode plot functionality works really well, especially if compared to similar functionality available in some oscilloscopes. We are only limited by the bandwidth of the waveform generator, but for most quick measurements, it is fine.