Keep It Simple.
The industry has been working for a long time to create a product that will make maintaining the water quality easier for the customer.
Most popular are ozonators. They are a simple device. The ozonator produces ozone gas. Ozone gas is a natural oxidizer (O3) that kills organics. That's a good thing. And for most the smell isn't that bad (ozone smells a burn smell). So depending on your hot tub, ozone gas gets injected into the spa and the ozone gas kills organics. Spas with 24/7 circ pump are most effective because the water is being constantly bathed in ozone gas.
Downside is the cost of an ozonator ($100-200), the life of the ozonator (3-4 years), and ozone gas can damage the items exposed between the water surface and spa cover.
Cost: Many find not having as much chemicals in the water is beneficial and the ozonator is good for that. So price isn't such an issue. Others are satisfied with current chemical usage and realize the cost of the ozonator compared to purchase of chemicals doesn't make an ozonator a wise choice for them.
Life: People can get fooled seeing "bubbles" thinking those are ozone bubbles; they are not. An ozonator uses a method to produce ozone gas. Over time that method weakens or stops completely. There are "ozone test kits" available and that is the only way to truly know if your ozonator is producing any ozone gas. But a 3-4 year life is most common. Some ozonators you can replace parts but most current production styles are throw away design.
Damage: The ozone industry has tried to address "off gas" or the amount of ozone gas that is release into the spa cavity between the cover and water surface. It still is an issue. Many have simply places something between the spa's top and cover to create a gap to release ozone and that solves the problem. In the summer that is a pretty good idea. In the winter you don't want your hot tub heat to escape. Ozone damage of above water level components like plastic and pillows can't be totally overcome. Some remove the pillows or treat the pillows to give them longevity.
Jacuzzi has addressed the Ozone issue with a totally new product; UV. Of course sanitizing water by UV has gone on forever from the sun. Its quite common in many industrial applications. Recently Jacuzzi made standard on most of their hot tubs a UV treating component called ClearRay.
What ClearRay does is simple. Water coming out of the circ pump is routed pass UV lamp. The UV lamp sterilizes the organics. It doesn't kill them, just makes them sterile. So they die and have no offspring. Pretty neat.
So there is no "off gas" to harm your pillows or knobs and such. There is no smell. You do have to keep your weekly testing going but you will use very little sanitizer and some just shock their water weekly and except for TA and PH, they are good.
COST is the biggest issue. The ClearRay bulb must be replaced annually at a cost of $75-100. Some other components might fail over time but typically for awhile you have a simple annual replacement. To retrofit into older hot tubs with a 24/7 circ pump is $450. Once this kit is installed you then go to the annual bulb replacement.
But for ease and smell and effectiveness with hot tubs with a 24/7 circ pump, the ClearRay is an excellent product.
For More Information About Clear Ray: Click Here