There are quite a few factors involved in how quickly they grow, and spread. Just a few of them include lighting, water motion, inhabitants, and levels of different ions and compounds present in the water. But, to answer your question with relation to some other corals, they're a on the high side of average. Of course, they do have the ability to grow and spread very quickly if ideal conditions are present. There are some really nice species of both zoos and shrooms, and they make really good beginner coral because they are pretty easy to take care of, especially if you are limited in terms of lighting and can supply good water motion as far as the zoos go. Shrooms don't really require a lot of water movement.
hth.