These shrimp are very cool, inexpensive, commonly sold, and best of all--they are not only good-looking, but also serve a great purpose! I highly recommend these shrimp to just about anyone who keeps marine fish, unless they are big fish that may prey on crustaceans.
The cleaner shrimp has an interesting symbiotic relationship with fish; when they have parasites on their skin, they come to the cleaner shrimp, who patiently picks them off, along with dead skin. They are harmless little guys and great to watch. If you get a few, they will be less shy and set up their own station on the live rock so that fish know where to find them. Mine even tries to climb on my arm and clean my hand when I put one in the tank! They are also greedy little buggers that will take a wide variety of other foods (not picky at all).
As with all shrimp, just watch water quality and copper-containing medications, such as those used for treating ich (copper kills inverts!), and you should be set. In fact, the cleaner shrimp in my tank actually keep my fish ich-free without quarantine or dangerous medications that can harm the reef. Great animals!