After renting ionic foot baths over the years, I've gotten some pretty nasty returns back.
Some are not the fault of the owner as they are so hard to clean. Some arrays are not easy to clean because of the plastic around it. Their toxic wastes are crusted on the arrays from usage and its even more nasty when its other peoples waste. These are usually the ones that have a wire going around it. Even using CLR on these it doesn't always clean it. The ones that clean the easiest have an open type design and I just dunk them in the CLR (calcium lime rust) solution and let it sit.
People say its not always the cost of the arrays but cleaning them which is the hassle. If you want a quickly cleaning array, please let me know if this interests you on my ionic foot bath quiz.