Does it take nonlinearity of strings into account? In the demo I can't really hear it and to me it ends up sounding like the comb filter synths you get without it.
Dev here! No, this version is an ideal string - no stiffness. Just meant to provide a fun and different way to think about sound design, rather than realistic string sounds (so the physical modelling branding is a bit of a misnomer). But it sounds pretty good I think! You can get some inharmonicity via numerical dispersion by reducing the accuracy (but in the wrong direction). I have a few other devices in the pipeline, at least one of which should include stiffness.
Physical strings have some stiffness and it causes overtones to not have perfect integer ratios of frequency. It's one of many things to consider that makes it sound a bit more natural.