(I asked the same question over at MRH Forums. I'll summarize answers both places.)
I've been looking at the Scenic Express Super Tree material and the Woodland Scenics Canopy Kit material. Super Trees is apparently "sea foam". I'm not sure what the plant name is for Canopy Kit, maybe yarrow?
The various descriptions and how-to I've read/watched uses similar techniques for both materials. Soak in (diluted) matte medium, optionally spraypaint the trunks, use matte medium or spray glue, apply coarse flocking, then leaf material.
So, any opinions on which is better? My inclination is that each has its place, and would be good to represent a select species of trees. Past that, I guess it gets down to cost for the material.
dave