The Disney World system is described
here and it is essentially a bromine system that uses electrolysis to convert bromide to bromine (similar to a regular saltwater chlorine generator pool that converts chloride to chlorine).
It's ironic that they claim that "chlorine and chlorine products are a main source of allergies associated with swimming pools" because more people are actually sensitive to bromine than to chlorine. It is true that an
improperly maintained chlorine pool can have disinfection by-products that smell or are irritating, but a
properly maintained chlorine pool has no such problems. In fact, a chlorine pool with Cyanuric Acid (CYA) in it is far less harsh than a bromine system, even though bromine is a weaker oxidizer at equivalent concentration (the key being that chlorine's effective concentration is very, very low in a properly maintained pool).
There is quite a bit of marketing hype in the cited article. One of the main reasons that commercial recreational water facilities like Disney use bromine is that it simplifies some other water maintenance parameters such as pH. If they had gone with a salt system to produce chlorine they would have had a much greater acid use then with bromine becasue bromine is active over a wider ph range. The biggest drawback is that bromine cannot be stabilzied against sunlight so their generating equipment needs to run more often ande the cells do wear out quickly. If I am not mistaken bromine generators use carbon electrodes.)
Aquasmart is a water purifier so does not sanitize the water and is described
here
This is a passive device much like a Nature2 or Frogger and is most likely based on copper sulfate and/or silver nitrate! Hardly chemical free! They do say on their website that chlorine or non chlorine shock is still needed! (In actual practice devices such as this need to be used with at least 2 ppm Free chlorine to maintain santized water in a pool!)
while Superior Aqua Systems Healthcare systems is a metal ion (silver, copper) system and is described
here. Silver will kill pathogens slowly so prevent uncontrolled growth, but are not fast enough to prevent person-to-person transmission (or bird poop to person transmission, etc.).
This is a standard electrio ionizer that puts metals in the water, once again hardly chemical free. Last time I checked metals were chemicals! There are drawbacks such as the staining issues (copper is what causes green hair, period!!!!) and the fact that metal ions are slow acting and in a pool you need a fast acting residual sanitizer such as clorine present!)
You can read more about alternative sanitizers in waterbear's Sticky
here.
Is there a particular concern you have about chlorine?
Richard