Is this meant to replace an installed office suite?

For most documents, yes, and for some it is not close. Letters, reports, essays, invoices, papers with citations and documents under review all work here. A hundred-megabyte document with linked spreadsheets, a template library driven by macros, or a layout tuned to a specific printer's driver belongs in an installed suite, and saying otherwise would waste your afternoon.

Will a document written here open correctly in Word?

Yes. The editor writes Office Open XML directly rather than through a builder library, putting styles, numbering, sections, headers, footers, notes, comments and tracked changes in the parts Word reads. A round-trip corpus of seventy-one generated fixtures gates that at 95% of constructs identical, and the build fails if it slips.

There are none, and that is a decision rather than a gap: a document that can execute code is a document that can execute somebody else's code. Macros in an opened file are stripped with a warning. What replaces them is a recorder for sequences of the editor's own commands — useful for repetitive formatting, incapable of touching your file system.

Why do my fonts look different from the installed suite?

Because a document names fonts rather than carrying them, and a browser can only draw what the device has. The font stacks name the open metric-compatible substitutes — Carlito for Calibri, Caladea for Cambria, Liberation Serif for Times New Roman — so line breaks hold where those are installed. Where they are not, the shapes hold and the metrics shift. Exporting a PDF with fonts embedded is the fix that always works.

Is there anything this does that an installed suite does not?

Three things, mostly by construction: it starts in about a second on a machine you are not allowed to install software on, it runs identically on Windows, macOS, Linux, ChromeOS and a tablet, and it has no update that can change your document's behaviour overnight. A locked-down work laptop or a school Chromebook is where that stops being a nice-to-have.

Browser Word Editor vs an Installed Office Suite

An installed suite is more capable and this is more portable. Where each one actually wins on .docx files, fonts, macros, review, privacy and getting started.