I talked to a plumber today and did some research. Here is what I have found.
First, I am getting my water tested. There is a local lab, if the water is not hard, then I can skip softening all together. I would just install a simple whole house filter and a hot water post-filter. This would be cheaper.
If I do have hard water (from the lines in the tub, I think I do), then the report will tell me what levels and I can shop for a filter & softener that fits my water's profile.
To avoid the ion-exchange (salt) softeners, there are two alternatives. One, electromagnet and two, crystal & nano membrane filters.
Magnets and crystals, sounds new-age. I am skeptical.
The plumber told me that the electromagnet type are "snake-oil". He has never seen one that worked and none of them are on the NSF.gov certified list. I am going to avoid these unless I find a certified one.
The crystal/nano filters, on the other hand, can be very effective and some are certified by NSF. The technology was developed by NASA and it supposedly works. The big drawback to these is the cost. The two that I found are each over $1000. So even it it doubled the life of the water heater it is not cost effective.
I am still looking/researching while waiting for the water test results. If you know of a certified salt-free water softener, let me know. Thanks.
Maybe this could be added as a product group?