It looks like this app has helpful functions for size, format, and transparency that you can't do with the built in chrome command all at once without probably piping it through inagemagik or something. And even then maybe this site renders the html responsively before rasterizing.
Actually Chrome does everything. Not via command-line switches however, you need to use the DevTools protocol. For example using Playwright. You get PDFs and PNGs of any size and resolution (PPI).
And I guess this is exactly what this service does under the hood.
