I bought the Scenic Express "Super Sage" kit (recommended for HO and larger

). This is essentially a box with sage bush pieces and whatever the "Super Trees" material is. I imagine that it's stuff that someone somewhere has in their backyard. It sells for $25 - the $40 kit includes a sprayer, matte medium, and ground foam in every color of the rainbow (only good if you're David Popp

).
It's hard to say how many trees this kit will make in n scale. A lot of the sage pieces are too big to be used as is, but they could always be split. But unless you're modeling redwoods, you'll have to break them apart. The "game" is to attach the super tree weed to the sage in a tree-esque fashion. Easier said than done. I actually split and grafted in pieces, and drilled holes to get a fluid look.
This is how they look assembled:

And painted and all groundfoamed up:

Note that the sage looks too much like a sand-beaten dead tree that you would see in the desert. But it looks organic and barky, too, so I like it. The kit is good for large trees, since there are few pieces smaller than what would be 2 ft in diameter for a real tree.