if you have a really good reason for a monopod, then the RRS head is the way to go. if you have not had experience with a monopod, it is not in any way a substitute for a tripod. a monopod can be useful (with experience) for sports photography with long lenses, but i can't think of much else
before you spend money on a RRS head (a ball head is completely useless), consider what you want to accomplish with the monopod