I used it instead of my GE over the summer going into LAX with my family (who don't have GE) and it worked a treat. Although the "helpers" pointing you towards the correct line were insistent that MPC was only for US citizens. They directed me to the usual immigration line which was probably over 100 people deep, so once they had moved on, we doubled back and joined the MPC line which had about 10 people in front of us and were through within 10 minutes.
GE is still faster and as Furryman said, you also get TSA pre.