Wouldn't this fail in a case where the unicode value was 2 or more bytes and the first or last byte happened to be the same?
Examples being:

U+00E9 (LATIN SMALL LETTER E WITH ACUTE, “é”)
• UTF‑8 encoding: 0xC3 0xA9
U+00EA (LATIN SMALL LETTER E WITH CIRCUMFLEX, “ê”)
• UTF‑8 encoding: 0xC3 0xAA

First byte is 0xC3 for both, but they are different runes

Failing Test case example:

Expect(Feast("ér", "êr")).To(BeFalse(), "Testing 'ér' vs 'êr'")

Could have a similar situation at the end, last bytes are equal but the runes are different