I copied that method from Pipes years ago and Rapid rooters for me just about every time, sometimes I drop them in a small cup of FF or coco, sometimes I will drop them older seeds in a cup of water to make sure they are viable and then if they dont pop in 48 hours I put them in RR's and they still pop I just dont get to see it. 

For me dropping a seed in Rock Wool is death sentence for the seed.