Where does this style work?

It works wherever plain text is accepted — bios, usernames and comments — because the letters are real Unicode characters, not a font.

Can I copy it together with other words?

Yes — copy the whole output and paste it next to plain text; every letter stands alone.

Line under every letter

Underline adds the combining low line (U+0332) under every letter — a real plain-text underline.

Y̲o̲u̲r̲ t̲e̲x̲t̲ h̲e̲r̲e̲