Some of our guys are on board that ship. I look forward to seeing where they go with it. I think I might hear it sometime since some of the locals in Singapore bought modules too.

Signed magnitude R2R has the same problem as normal R2R (regardless if Soekris feels this isn't the case) but it just shifted to half the output voltage AND is also non symmetrical.
The problem is thus shifted, and doubled, as it occurs differently on the positive and negative half of the output signal, so is not eliminated nor has it become less relevant.
The 'crossover type distortion' is still there and equally 'bad' and still can affect small signals.
Small signals are superimposed on larger amplitudes and is thus not restricted to the '0V line' for AC signals.
Very similar to amplifiers that are partly in class-A and haven't been designed that well.
It isn't anything 'new' or revolutionary either the 15 year old PCM63 also had this topology but called it colinear.

You could improve this by changing the actual output codes (forward correction) to be closer to the desired output voltage but you would have to do measurements and apply it on each individual DAC/channel and will be hard to do yourself unless you have the needed test equipment and programming stuff.
It will be a different correction for positive and negative halves of the output signal as well.

As I mentioned a few pages back.... even 0.01% parts for the MSB isn't enough.

Still, even with those linearity errors the DAC will, most likely, still sound excellent to many ears.
As it doesn't have a proper reconstruction filter (nor do other NOS DACs in general) for lower bitrates the >6kHz signals will still suffer from 'roll-off' which makes these DACs 'mellow' sounding. That roll-off isn't 'fixed' though and highly depends on the output frequency/sampling frequency relation (whether they happen to be in 'sync' or not at specific points in time).
So while Kees's (Metrum) theory may be valid for 1kHz sine wave signals (the drivers and ears combined are acting as a >8th order smoothing filter) the drivers and ears do not act as a proper reconstruction filter (it needs to be ringing to do so) at all and thus the higher frequencies DO sound different from the signals that had been recorded.

Of course some roll-off seems to be preferred by many so may be a blessing to some and be viewed as 'increased fidelity' by (varying) lack of upper treble.

Added LH DAC vid to first post for reference and further discussion should it arise.

Slots and stuff, see that TONS in multimeter and bench designs, but none in audiophool stuff and I don't remember seeing them in AGD DACs too. Ground plane and clock layouts are very thorough and again, I don't see them much in the bareboards I looked at in my limited exp.

Audio-gd use separate boards for digital and analog altogether (in the TOTL designs, at least).

The clock trace thing is basic electronics, though. You obviously want them to be equal length for both DACs.
I don't like to see different shapes for both traces, though. Placing the clock in the center and a mirror design is more reassuring to me.