Buy 2. One for each leg to help support your legs while sitting cross-legged. If kneeling is your thing you can stack two and adjust the height. Be sure to change the quantity to "2".
Buy 4. Two blocks for under your seat and two blocks to support your legs.
Be sure to change the quantity to "4".
Made from the same stuff as foam yoga blocks this meditation "sit system" was design people looking for a more supportive way to kneel or sit cross-legged.