$function_name() vs call_user_func($function_name)

http://dikini.net/php_design_patterns

で、「$callable(...)」と「call_user_func($callable,...)」「call_user_func_array($callable,...)」について言明していた。
あいかわらず英語の内容を翻訳する気はゼロだけど、ニュアンス的に「$callable(...)」はキモイから使うなって言ってるのか？

よくわからないけど、ちょっと実行速度だけ適当に測定してみた。

define('REPLAY_NUMBER', 100000);

$function_name = 'test_function';

$time_a[0] = microtime_ex();
for ($i = 0; $i < REPLAY_NUMBER; ++$i) {
    $function_name();
}
$time_a[1] = microtime_ex();

$time_b[0] = microtime_ex();
for ($j = 0; $j < REPLAY_NUMBER; ++$j) {
    call_user_func($function_name);
}
$time_b[1] = microtime_ex();

echo 
        "<pre>\n", 
        "time_a is ", ($time_a[1] - $time_a[0]), "\n", 
        "time_b is ", ($time_b[1] - $time_b[0]), "\n", 
        "</pre>\n"
    ;

function test_function() {
    sleep(0.001);
}

function microtime_ex() {
    $mtime = explode(' ', microtime());
    $msec = (float) $mtime[0];
    $sec  = (float) $mtime[1];
    return ($sec + $msec);
}

[1回目]
time_a is 0.32629895210266
time_b is 0.5169689655304

[2回目]
time_a is 0.38656997680664
time_b is 0.59860301017761

[3回目]
time_a is 5.143630027771
time_b is 0.83590197563171

[4回目]
time_a is 0.33151888847351
time_b is 0.5154390335083

[5回目]
time_a is 0.43265199661255
time_b is 0.57433485984802

「$callable(...)」の方が速度だけでいえば早いのか？