I had to get the Xfrog Tropics set for the documentary I'm working on, and thus far I have been really impressed with the plants. There was one single issue with one single .obj in the whole set, and it took about thirty seconds to fix. The textures are nice and the models are very detailed.
However, unless you are planning to do an extensive series of images based around the included plants, and/or are going to make money off of using them, the rather high price wouldn't seem justified to me.