I have bred many species of fish (FW & SW) and the various sizes of OGP and various sizes of live foods were an effective way for me to raise fry. I have never used OGP as a coral food so I cannot speak to that part of the question.
To use, I would stir the powered food into a small container of tank water and then add it to the tank - with minimal to low flow the particles stay suspended for a while. In a reef system the CUC will take care of what is left over. Also by premixing, this gives you the option to target feed any type of powered food to corals by using a turkey baster (or comparable). In fry tanks I then come back and siphon any amount that is left over from the bare bottomed tank.