Those who meditate on ome with a stress on umm they will attain to Virat. Those who emphasize on u will attain oneness with Hiranyagarbha the cosmic mind after death. But those who concentrate on the silence at the end of ome concentrate means they realize the meaning of that I am Brahman.
Swami Sarvapriyananda teaches one of the shortest and most profound upanishads accompanied by Gaudapada's Karika. This lecture covers Karika 22-23 and Mantra 12.