These two products are compared constantly and only one of them is a softener. A salt based unit removes calcium and magnesium from the water by ion exchange. A salt free unit leaves them in and changes their behavior so they deposit less. Deciding between them is really deciding which of the hard water complaints you actually want gone.
What each one does mechanically
A salt based softener passes water through a bed of resin beads holding sodium, which swap places with the calcium and magnesium. When the bed is loaded it regenerates: backwash, brine draw to strip the hardness off and restore sodium, then rinse. A salt free conditioner passes water over a bed of polymer beads whose surfaces nucleate microscopic hardness crystals that release into the flow, so hardness travels through as suspended seed rather than bonding to hot surfaces.
What changes in the house
Both greatly reduce scale in the heater and the appliances, which is why both are sold. Only the salt based unit changes everything else: lather, soap scum on glass and tiles, spotting on taps and shower screens, stiff laundry and the tight feeling on skin after washing. All of those are caused by the minerals being present, so a conditioner leaves them exactly as they were. A hardness test after a conditioner reads the same as before, and that is the expected result rather than a fault.
What each one costs to run and to install
The salt based unit needs a drain connection, a supply of salt carried and loaded, space for two tanks, and it sends water to drain on every regeneration. It adds sodium to the water. The conditioner needs no drain, no salt, no power in passive designs and sends nothing to waste, but requires a sediment prefilter and, on chlorinated supplies, carbon ahead of it to protect the media, which is replaced every few years rather than serviced.
Choosing between them honestly
Take the salt free route where there is no drain within reach, where a septic system or local rules restrict softener discharge, where sodium is unwanted in the drinking water, or where the complaint is genuinely about appliance scale. Take the salt based route where the complaint includes how the water feels, looks on glass or behaves with soap, since only removal fixes those. The USGS classes water above 180 mg/L as calcium carbonate as very hard, and expectations matter more at that end. Our salt free guide compares the specifics.
Questions people ask about salt free vs salt water softener
Is a salt free unit a softener?
Not technically. It leaves calcium and magnesium in the water and only reduces their tendency to deposit as scale.
Will a salt free system improve lather and reduce soap scum?
No. Those are caused by the minerals being present, and a conditioner does not remove them. Only ion exchange does.
Why choose salt free at all?
No drain needed, no salt to buy, nothing discharged to a septic system and no sodium added, with good protection against appliance scale.
What maintenance does each need?
The salt unit needs salt, a drain and periodic brine tank cleaning. The conditioner needs a sediment prefilter, carbon on chlorinated water and a media change every few years.