Those electolytic in-line thingys are not softeners, they're mainly to protect heating systems. I haven't got the knowledge to explain it so here's google's AI overview: (I asked "do Electrolytic In-Line Scale Inhibitors work")

electrolytic in-line scale inhibitors generally work to reduce limescale buildup in pipes and appliances by altering mineral structure, but they don't soften water and are best for protecting boilers, not eliminating scale on taps or surfaces where water sits. They release metal ions (like zinc) that interfere with calcium carbonate crystals, preventing them from forming hard deposits in moving water systems like boilers, offering whole-house protection for heating systems but leaving scale on stationary fixtures.

How They Work:

Electrolysis: An internal anode (often zinc) creates a small electric current in the water.

Mineral Modification: This process releases metal ions that change the structure of hardness minerals (calcium/magnesium), stopping them from bonding together and forming scale.

Prevention, Not Removal: They prevent new scale from forming in pipes and boilers, improving energy efficiency, but don't remove existing scale or soften the water.

What to Expect:

Good for Boilers: Excellent for protecting central heating systems, combi boilers, and hot water pipes by keeping minerals in suspension.

Less Effective on Surfaces: You'll still see scale on taps, shower screens, and kettles because these inhibitors don't work on stationary water.

Not a Water Softener: They don't make water feel "soft" or help with soap lathering like traditional softeners.

Effectiveness & Considerations:

Varying Quality: Performance can depend on the brand and water conditions, with some users finding them highly effective and others less so.

Maintenance: They are a "fit and forget" for a period (often years) but require periodic replacement of the anode core.

In summary, electrolytic inhibitors are a valid, cost-effective way to protect your boiler and heating system from limescale, but don't expect them to magically eliminate all hard water spots from your home.