I use the latter extensively and am quite happy with it. The listed advantages of Tectonic are somewhat debatable:
> Tectonic automatically downloads support files
I use a full TeXLive distribution in a Docker image. But this is a clear advantage on regular desktop setups, although I'd argue most people don't notice that texlive is 4GB+. MiKTeX does downloading on-the-fly, too.
> Tectonic has sophisticated logic and automatically loops TeX and BibTeX as needed
Latexmk does this too. BibTeX is outdated (use biblatex+biber), I hope Tectonic is not hardwired to it.
> doesn’t write TeX’s intermediate files
Sounds terrible! For a long document I maintain, a cold run takes 8 minutes. A "cached" run (all auxiliary files present and somewhat up to date), it's below 3 minutes. It only says this is the default setting, but it would be a devastating default in my case.
> The tectonic command-line program is quiet and never stops to ask for input.
Okay that sounds nice, but I've used the interactive "can't write to file X.pdf" many times before, when the PDF to write to was locked for writing (open in PDF viewer). It saves aborting the entire run and starting fresh.
> Thanks to the power of XeTeX, Tectonic can use modern OpenType fonts and is fully Unicode-enabled.
Nice, but is this Tectonic-specific? I use latexmk with lualatex. The latter is better than xelatex (microtype, contour, memeory management, lua integration, ...). If Tectonic is hard-wired to xetex and doesn't allow lualatex, this is a big downside.
The remaining points are nice, especially the GitHub actions stuff. Though I just use the same Docker image there that I use for local development.
> BibTeX is outdated (use biblatex+biber), I hope Tectonic is not hardwired to it.
While I prefer biblatex and biber, some journals and conferences require BibTex.
