Dragon juice and Roof snot are not comparable products. Dragon juice is used as a multi-purpose degreaser and is a much higher cost product, really serves no purpose for roofs. Roof snot is a surfactant used to "bite" your SH onto the shingles and is very reasonably priced. Great additive to SH for roof cleaning.
Have used Dragon Juice on many a roof....works great...we mix it 5:1 and run it through our proportioner and works great. Really sticks good when you want or need that and also seems to really help in the cleaning. We generally only use it on roofs with a steep pitch. One thing you do not want to do is mix DJ with other soaps. We still use Roof Snot too and love it.