My only complaint is that the install NOR the documentation bothers to mention that the install process is going to bleed past the confines of this add on and that it is going to actually modify other areas of a forum.
Obviously, people use custom styles on their forums all the time. This is not some new or limited occurrence. Any and all issues with custom styles could be easily addressed in the documentation.
In my opinion the install oversteps its bounds when it makes unannounced changes to non-gallery parts of the forum.