The question is whether quantization error should in fact be random or whether it should follow Benford's Law as many natural phenomena do. Adding TPDF noise certainly works but maybe it just happens to approximate Benford's Law better than the other density distributions. Interesting topic for further research.
TPDF first decorrelates the quantization error, and then decorrelates fluctuations of noise making the noisefloor totally and utterly uniform. Sounds fade under it with no alteration of their tone or amplitude (VERY not the case for truncation, obviously)
I do make a TPDF, also, for those who like that. Bob liked my 'PaulDither', a simple highpass TPDF. Oddly, by making a TPDF with two noise sources and a 1 LSB offset, I ended up with a TPDF that people thought sounded better than any other TPDF: turned out for some reason it was producing half an LSB of DC offset, so the noisefloor was distributed across three 'bits' instead of just two, and one of the 'bits' functioned as zero (rather than the dividing line between the bits). Anyone who figures a half-LSB of DC offset is a dealbreaker is welcome to use somebody else's dither ;)
There's no GUI as there's nothing for one to do (and it will help the plugin retain usefulness: less to break).
Dave, I'd love for you to test NJAD (and NJAC) by seeing how far you can hear into the noisefloor, on any content, in any testing situation. From where I'm standing, I've made a lot of wild dither/noiseshaper experiments. I'll never forget how you hated 'Ten Nines'. But that was what, decades ago? And I've learned a lot, and I think NJAD will perform a LOT better. As you might expect with the noise profile it has, any weak point would be how it handles near-Nyquist information. I trust that you can hear that stuff, so I'm very interested in your reaction.
For anybody who's not super-sensitive to extremely high frequency information, NJAD has a lower noisefloor than anything, and lets you hear the (unaltered) sounds fading into the noisefloor better than anything. It's way, way, way quieter than TPDF. (bear in mind that if you're doing all your work dithering to 24 bit, it would be madness to expect anything like a 'huge improvement': anything we do at that level is more about mitigating incremental damage and incremental noise buildup)