The hardest part of this comparison is not the technology, it is the evidence. An ion exchange softener produces a change you can measure in a glass with a test kit. A salt free conditioner produces a change you largely cannot, which is not the same as no change, but it does mean the two categories have to be judged by different standards and marketing exploits the confusion.
The test that separates them
Take a hardness test before the unit and after it. On an ion exchange softener the difference is unmistakable: hardness minerals have been physically removed and swapped for sodium, so the treated sample reads soft. On a salt free conditioner the two readings are the same, because the minerals are still there. That is not evidence the conditioner is failing, since it was never meant to remove anything, but it does mean that anyone selling you a conditioner on the basis of a hardness test result is selling you something it cannot deliver.
What a conditioner claims, and how it could be shown
Template assisted crystallization and similar approaches encourage hardness minerals to form stable crystals in the water rather than deposits on surfaces, so the claim is about scale adhesion rather than removal. That is testable, but not with a home kit: it is demonstrated in controlled scale formation trials rather than by anything a householder can do at the tap. The honest evidence to ask for is independent testing of scale reduction under a defined protocol, and the honest domestic proof is the state of the kettle element and the shower screen a year later.
Claims that should make you cautious
Be careful with any conditioning product described as a softener without qualification, with claims that soap will lather better or that existing scale will disappear from pipework quickly, and with any product sold on a hardness reading. Be equally careful with softener sellers who imply sodium levels are dangerous for ordinary households. Both categories have legitimate uses and both are oversold, and the tell in each case is a claim that belongs to the other technology.
Judging by the symptom you wanted fixed
In the end this is decided by outcome rather than argument. If the reason for buying was soap, laundry feel or removing existing scale, only removal delivers it and ion exchange is the technology. If the reason was protecting a water heater and stopping new scale, conditioning may well deliver it and does so without salt, a drain or power. Set a check in a year: look at the kettle, the shower screen and the heater. Our salt free softener guide compares the units and what each publishes about its testing.
Questions people ask about salt free water softeners vs salt
Will a hardness test show if my conditioner is working?
No. Conditioners leave the minerals in the water by design, so the test reads unchanged. Only ion exchange changes a hardness result.
What evidence should I ask a conditioner seller for?
Independent scale reduction testing under a defined protocol, since that is the claim being made. A hardness reading is not relevant to it.
Does salt free equipment remove existing scale?
Not in the way removal does. Softened water gradually clears existing deposits; conditioning is mainly about preventing new ones from sticking.
How will I know in a year which one worked?
Look at the kettle element, the shower screen and the water heater, and compare with how they were before. That is the outcome you bought.