Peter Mitchell

Good job on highlighting the necessity of the mb_* extensions for handling UTF-8 strings. However I disagree with your second assertion, the best way to compare string length in PHP is the obvious way. By making a micro-optimisation such as this early, you lose a communicative aspect to your code.

$str = 'hello!';

if (isset($str[5)) {
    // ... $str is less than or equal to 5
}

if (mb_strlen($str) <= 5) {
    // ... don't need a comment here, the intention is obvious
}

What if I want to check if a string is greater than 6? Then I am back to using mb_strlen.

These cases should only be targeted for optimisation when actually needed, by taking this practice into common use you may lose more than you gain.