Singleton design pattern and pool design pattern to increase efficiency of code

Singleton design pattern

<?php
class produkt_pool
{
    protected static $instance = array();
    
    public static function get_instance($pid)
    {
           if(!isset(self::$instance[$pid]))
           {
               self::$instance[$pid] = new produkt($pid);
           }
        return self::$instance[$pid];
    }
//another type of instance if instance was not array
public static function &Instance()
		{
			static $instance;
			if (!isset($instance))
			{
				$c = __CLASS__;
				$instance = new $c;
			}
			return $instance;
		}
}


class produkt
{
    public $data;
    public function __construct($pid)
    {
		echo "<br />PID ",$pid," is initiated<br />";
        switch($pid)
		{
			case '1': $this->data = array("test"=>3,"Value"=>4);
			break;
			case '2': $this->data = array("test"=>20,"Value"=>50);
			break;
		}
        return $this;
    }
    
     public function __call($method, $arguments)
    {
        if(true === array_key_exists($method, $this->data))
        {
            if(is_array($this->data[$method]) && count($arguments) > 0)
            {
                if(true === array_key_exists($arguments[0], $this->data[$method]))
                {
                    return new self($this->data[$method][$arguments[0]]);
                }
            }
            return $this->data[$method];
        }
    }
    
}
/*
$data = new produkt(1);

echo $data->value();
*/
echo "INIT PID 1<br />";
$data1 = produkt_pool::get_instance(1);

echo "<br />";
echo "PID 1 TEST",$data1->test();

echo "<br />INIT PID 2<br />";
$data1 = produkt_pool::get_instance(2);

echo "<br />";
echo "PID 2 TEST",$data1->test();


$data1 = produkt_pool::get_instance(1);

echo "<br />";
echo "PID 1 VALUE",$data1->Value();


$data1 = produkt_pool::get_instance(2);

echo "<br />";
echo "PID 2 VALUE",$data1->Value();

echo "<br />";
echo "<br />";
echo "<br />";
$data = produkt_pool::get_instance(1);
echo $data->test(),"<br />";
echo $data->Value(),"<br />";