I have a container of Natty's blue that I layer 3 times, every 6 weeks or so. I have quite a bit left, I was thinking of trying some P21S 100% since I have read good things about it. I have a black metallic finish. Is there a noticeable difference between the Natty's blue and P21S that would make it worth spending $50? Or should I just be content using up my Natty's blue. I also use FK425 over the Natty's which I find to leave an incredible slickness and shine. Help me save, or make me spend. Thanks.