If you need the MP3 file permanently, pay the $1. It’s cheaper than a coffee, supports the artist, and you get a clean, high-quality, legal file without malware risks. If you’re okay with only listening online, use Spotify or YouTube for free.
“All of Me” is copyrighted commercial music. It is not legally available as a free, permanent MP3 download from official sources (like the artist or label) except during rare promotional events. Any website offering a free permanent download is almost certainly illegal (piracy) and may contain malware.