No expert, but had one put in last year. I think the size is pretty much the same until you get to a really big house. Less usage should just mean you will re-generate less often (use less salt). It cost me about $1,800 to have one put in (the higher quotes were $2,400 & one was much higher - brand name Culligan) - it might cost you a little more to make the connections or tees into your existing piping (I had that done while doing some other plumbing work, so there was a place for the guy to connect to). They connected it all up, ran their lines to the softener and then a little flexible line which they had to run over to where I had a Y in my plumbing where they could connect the drain. Just 2 of us use it, mine regenerates every 2 weeks - I use about 2 bags of salt every 3 months. The salt is $10 or $12 something like that per bag. Made a big difference in the scale build up on the fixtures, soap seems to take a bit longer to properly rinse (but that might just be me), no difference in taste. Interesting side note - if, a while after you get your softener, your HOT water starts smelling like sulfur, it's because of the difference in the chemical reaction with the anode in your water heater (from the reaction that takes place when the water is softened - I'm not a scientist so I can't go deeper than that unless I start looking stuff up). The anode is a sacrificial rod that keeps the inside of your water heater tank from corroding. If the sulfur or rotten egg smell comes from just your HOT water, consider replacing one of the anodes in your water heater (they often have more than one) with a powered anode. The difference in the way the anode works stops the sulfur smell from happening within a couple of hours. Hope this is helpful Good luck

Every water softener does what it’s made to do. Pricing does not determine quality. When I sell a water softener, it’s always a 2 cubic foot mineral bed. The reason for that is, the larger the bed means the softener can go longer before it needs to clean itself. I live in California and there is no price difference between a 1/2 cubic foot and a 2 cubic foot softener. They all use the same control head.