An ISO file, or ISO image, is an archive file that contains an image of an optical disc, such as a CD, DVD, or Blu-ray. These files are often used to distribute operating systems, software, and game images over the internet.

What (e.g., Arista switch, Android phone, VM) are you using this for? g., to enable serial console access)?

A "better" download is a "correct" one. Once downloaded, compare the file's hash against the official documentation to ensure the ISO wasn't tampered with during the transfer. Use a Download Manager