I have had one customer who had me add a UV system in-line with ozone on a HotSpring spa. I found a good unit, made for hot tub use, and plumbed it between the heater and the ozone injector, and then wired it in.
Several years later, there was a Ground Fault, tripping the breakers, and I traced it to the UV unit. Simple job to remove it, and from the looks of it, it had been bad for a very long time. The customer had noticed no change whatsoever.
HTH