Ok since it's supposed to work fairly quick (3 months) I may give this stuff a try and find out for myself.What happens with a lot of them, is that after they start rolling, they're paying a lot more close attention to the bald spots than they were before. They notice the miniaturized hair they didn't notice before and think "OMG it's working!"
So they come on the forums and tell everyone about this incredible progress they're seeing, but after 4 - 6 months and several haircuts and realizing the "results" aren't getting any longer. They tap out to save face.
What basically all evidence, both user-reported and clinical study shows, is that if you're not seeing serious results after 3 months (and you've dermarolled correctly) then it just simply isn't working.