Slab tendon steak is also known as oyster meat. With more lean meat and less fat, the meat is more tender and has a texture straight out of filet mignon. There is also a tender tendon in the center, unlike the white tendon that you can't chew, the plate tendon also has a little bit of popping and crunching after it's been fried and grilled.
The sirloin steak meat is thicker, with higher fat content than filet, slightly thicker fiber, and some connective tissue and fascia.