What effect are you looking to achieve? Rust stains, sulfur smell? Less detergent for laundry?
Depending on your water, and the results you want, will tell you what systems might be a good fit.
I purchased our home in 1986. In the 90's, our water softener (used salt) gave out.
I researched everything I could (harder job before the Internet got rolling like it is today).
I built myself, a magnetic system, to treat the water. We no longer have any rust stains, and it even keeps the sulfur smell down most of the time. Some years, we smell it once, some years, we never smell it.
Most magnetic systems do not work, because you need to study what you are trying to achieve, and how your plumbing system is set up. Magnetic systems, are not one size fits all. If you figure out how to make one, and install it yourself, the systems costs nothing to operate, and lasts a lifetime.
The build cost of mine was under $100
If you do it wrong, it will not work, and you are wasting your time.
I am sure there are now sources all over you tube, showing how to build one.
I know for a fact, they work, if properly installed.