My opinion is that water softeners work, and magnetic conditioners are like magic, or wearing a copper bracelet for rheumatism - it doesn't work, but if you believe in it, you will feel better.
You will get people saying a water softener might go wrong and release salt into the boiler by mistake, and your boiler manufacturer may say warranty does not apply if softener used.
However, I have a softener, very pleased with it, the way it works prevents it from releasing salt or chlorides, but I can't swear they never go wrong.
The salt does not go into the water you use. The water goes through a resin which absorbs the calcium. When the resin is "full" of calcium the machine stops supplying soft water, turns a valve which disconnects the resin tank from your system, sucks salt solution into the resin and this washes the calcium out. It then rinses the salt out of the resin and down the drain, and only when finished does it again allow water through the resin and into your system. While the refreshing is going on it operates a valve which either allows you continue using your system with hard water, or supplies softened water through a second back-up resin container.
If I was buying another, I'd get the metered one, which recharges the resin accurately according to amount of water used, rather than by the calendar.
The amount of salt they hold just means you have to top-up the bigger ones less frequently as they don't run out so often.
They are as easy to plumb in as a washing machine. Put it where you can easily get to it while carrying a 20kg sack of salt granules, and where you can clean up any salt granules you spill without it getting into metal or concrete. A kitchen floor is probably OK. If in the garage put some vinyl flooring down and keep your tools away - a speck of salt will make them rust or corrode through.
