If you're in the position of having hard water with more minerals in it than you can stand (or more than is healthy for your plumbing), a hard-water treatment is the logical next step. But if you're trying to choose between a conventional ion-exchange treatment and the much simpler magnetic treatment, you'll need to analyze your reasons for treating your hard water carefully. Here are three differences between the two that will help you decide which water softener is best for your situation and your goal.
A magnetic water treatment, since it's much simpler and doesn't involve any actual machinery, can have a very low cost. It's true that this lower cost may come with a correspondingly low reliability rate, since magnetic water treatment works better for some people (and some wells) than others. Upkeep costs are lower for a magnetic treatment as well, since you don't have to periodically buy bags of salt to recharge things.
The mechanism is totally different for a magnetic treatment than for ion exchange. Ion exchange actually removes the bothersome minerals from the water, replacing them with salt ions. This reduces the mineral taste, although it also leaves the water with a distinctive "softened" flavor. Since magnetic treatment doesn't remove the minerals at all, simply "realigning" them so they don't produce buildup, it affects the flavor much less.
Some people claim that magnetic treatments work very well, while others may be dissatisfied with the scale reduction they see in their plumbing fixtures. An ion-exchange softener, since it actually removes the minerals, is more reliably effective at reducing scale, although some experts feel that softened water can also harm your plumbing by leaching substances from it and require additional filtering before you drink it so you don't get heavy metals in your diet. Magnetic treatments are much less invasive, meaning they're less likely to cause these unwelcome results, but they also don't keep your water from tasting like minerals.
These three differences show how substantial the gap is between magnetic hard water treatments and the more common ion-exchange water softeners. If you're looking for a reliable method that will remove all traces of calcium and magnesium, ion exchange may be for you; but if you're sensitive to salt and don't mind the mineral flavor, you may prefer to start out with magnetic treatment and see what that does for your plumbing.