I believe you, but I'm curious what the "quick testing" consisted of.
Much more interesting to me: Are there any ADCs that you have quick- or slow-tested that are "good"? "Good" value, as the Behringer DAC is, or just straight "good", independent of price.
I have been using the Focusrite Forte which is a two channel recording interface. It has lower noise and distortion than most affordable devices. It was $400 or so originally, but has been discontinued. Used ones crop up for $250 or so. Some report issues with Macs they work fine with Windows. If you have a Mac with a Thunderbolt interface, the Focusrite Clarett line uses the same ADCs and circuitry. One thing handy about the Forte is gain is done in exact 1 db steps. Makes repeating tests exactly much simpler than having an analog adjustment knob for gain.
An Audient ID14 is a similar interface available for $299 new. The specs are similar or only slightly worse.
You could get a Motu 8A (which one of the members here has) or 624. The 624 is fewer channels with 2 microphone preamps and the 8A is more channels without mic inputs. These have slightly better specs than the above gear, are a bit overkill just for testing and go for $795. These also do gain in exact 1 db steps.
Plenty of good recording interfaces would do okay for basic testing to confirm operation is okay. The issue is they have similar distortion and noise levels to the gear tested. So ultimately part of the artifacts will be the testing ADC as much as the device under test. The Behringer on the ADC side is substandard for these purposes. Though other Behringer gear might be better.
I also don't much care for RMAA. It isn't too much trouble to make your own test signals and evaluate them with Audacity and WaveSpectra or similar free software. It just isn't automatic like letting RMAA run itself and spitting out parameters.
You can look at the budget DAC review of the HDMI switcher I posted for some examples.
Also here are a couple of examples of being able to make your own test signal. Click on the images for an enlarged view. Each panel has a single frequency sweep on the left and a twin frequency sweep on the right with the two frequencies always 1 khz apart.
This is using a spectrogram view. I think I chopped off the frequency scale by accident, but it shows 0-24 khz bottom to top in this case. In the first one the floor is -100 db. Anything below this level will not show up.
It looks perfectly clean other than the sweep signals. So any harmonic distortion in the left half and any intermodulation distortion in the right half is below this level. Usually if it is lower than this you have no reason to care.
Now I drop the floor of the spectrogram to -120 db. You'll see a slightly steeper sloping line in blue above the main signal. This is the third harmonic distortion which lies between -120 and -100 db. The oppositely sloping faint blue line is low level aliasing as the filter of the tested device isn't quite as steep as needed to eliminate all aliasing.
Now the spectrogram floor is dropped to -130 db. You'll see multiple faint blue lines. In the left side you see 2nd, 3rd and 4th harmonics. In the right you see additional low level IMD products. The device being tested btw was an old Tact RCS 2.0 room correction unit set to flat response.