A few things to remember about these little guys.
They are naturally short lived. Most common reported life span is around three years max.
They easily disappear into overflows, power head or filter intakes, over the side of the tank etc. or into larger fishes mouths in the case of tanks with more aggressive specimens with no respect for there cleaning abilities.
They are not immune to parasite infestation themselves.
The cleaners, be they shrimp wrasse or goby, are of negligible value for curing or preventing ich.
The positives.
They are inexpensive and will breed in captivity and will attempt to clean any willing fish.