Gain-Phase measurement without dedicated equipment

Just use a dual-trace scope and a function/sine generator; and trigger the scope sweep from the function generator's "sync" output.

At each frequency of interest, adjust the scope's "variable time" knob (you do have one, right?), to use exactly NINE horizontal divisions per input sin cycle; thus you have exactly 40 degrees per division; most scopes have either 4 or 5 small time-tics per major division, thus you can easily interpolate to 1 or 2 or 4 degrees.

ADVANTAGES? you get to WATCH how the circuit performs over the tested frequency range;

(1) if the time delay is not absolutely stable at each frequency, you probably have spurious oscillation, to be debugged. Maybe ensure the bypass caps are installed, so the 2 meters of wire from powersupply to circuit is not causing problems

(2) you get to look for clipping at all frequencies

(3) at some frequencies, because of poles and zeros, you'll see very small output; is the RANDOM NOISE AND POWER SUPPLY NOISE about what you predicted?

(4) you get to discover SLEWRATE limiting

(5) you get to see blatant cases of distortion; 2nd order causes lopsided output sine shapes; crossover distortion in a class_A? cannot happen, right? but if you do?

SUMMARY: you are responsible for all modes of behavior of your system. Be responsible. Examine the waveforms. Otherwise your boss will have to hire a consultant later, to clean up the mess you made.

What you're buying in the Bode-100 or the 4194 is the convenience of having it all in one box, easy to use, with specified performance.

When you roll your own, with a signal source, two ADC channels, and some software to control and analyse, you're taking some of that burden on yourself.

It would be very educational to build your own.