We have a local rail jam every 2 weeks in our area using snowgel.  there are a couple of people, like freezed who have not had positive results, but there are 100's that have.  Not sure what is different about thier set up, but I can assure you, that we had to scrape a lot of the gel off our set up to slow it down.
You can see how little gel was used in the top and middle pictures, click on them.