Unlike the installer version, the "portable" variant runs entirely from a USB stick or a local folder. It writes zero data to the Windows Registry and leaves no traces on the host machine.
Rufus supports a massive array of file systems. While most users will stick to FAT32 or NTFS for Windows installations, Rufus 3.10 also supports:
Very stable for its intended use. I’ve created ~200 bootable USBs with Rufus portable versions, and version 3.10 had no major bugs. The only crash I saw was when writing a corrupted ISO — which is expected.