in_array vs array_unique

gistfile1.php

<?php
    $start = microtime(true);
    $lists = array();
    for ($i=0; $i<1000000; $i++) {
        $key = rand(1,500);
        if (!in_array($key, $lists)) {
            $lists[] = $key;
        }
    }
    $end = microtime(true);
    echo $end - $start . "\n";
    
    
    $start = microtime(true);
    $lists = array();
    for ($i=0; $i<1000000; $i++) {
        $lists[] = rand(1,500);
    }
    $newLists = array_unique($lists);
    $end = microtime(true);
    echo $end - $start . "\n";