DIVX is dated: phones, browsers and many editors do not open it. MOV is what Final Cut, iMovie and other Apple tools prefer. A DIVX file usually holds DivX video, usually with MP3 or AC3 audio. DIVX is at home in old downloaded films and DivX-certified players; MOV is the usual choice for recording and editing on Apple devices.
The defaults suit most files. Under Options you can lower the resolution, trade quality against file size, remove the sound and trim the start and end. This is demanding work for a browser: a long or high-resolution file can take several minutes, and your device does all of it, so keep the tab open.
This pair uses the compatibility engine, ffmpeg built for the browser, because DIVX is not handled by the browser's built-in codecs. It is a one-off download of about 10 MB that the browser keeps, it is slower than the built-in codecs, and it takes files up to 1 GB.