I actually used those exact Matrix midcaps from Evike and they work fine on my Umarex G36CV... but they look different in real life. I ended up selling them because I liked the Magpul ones better. They have a bit of wobble side-to-side but I fixed that by using some hockey tape inside the magwell. They are still feeding well to this day.
http://www.evike.com/product_info.php?products_id=37666