I've never personally applied it, but I think our main targets are mature trees that have either begun to decline, or are showing signs of stress, or just plain dont have any reason to be putting alot of energy into new shoots.
We do this big white pine in the middle of a courtyard area, not sure if its due to the GR, but the new growth has looked semi chlorotic for several years, but you can definitely see the stunting of the growth in the shoots. I personally think it really detracts from the usual look of a pine, but thats just me. Any large pieces come off the pine and its taking some pieces of brick mills with it.
I think I've seen the effects of it work to some extent on white and red oaks, as far as being up close to see new shoot growth at the tops of the trees, but otherwise, as I'm not the applicator, unsure of where and what its being used on, and what effectiveness it has.
There are some hemlocks we do, with a bunch of rhododendron max. under it, and I will tell you what, it definitely regulates the growth on the rhodies! lol