I purchased a system from Ohio Pure Water. I saved at least half over what it would have cost to have a local company come out and install identical equipment. The system has a Fleck demand control valve and has been trouble-free for several years now.
Note that the bigger the softener resin tank, the better the flow. And it's better to get a short, fat tank than an tall, skinny one of the same capacity.
Note that the way the demand softeners work is to meter the amount of water through unit, then when the capacity has been used up, it will wait until the timer says it's time for regen. So they always regen in the early morning, assuming you keep the timer adjusted properly.
Softeners are normally set up to only regen about half their capacity. That way salt isn't wasted since the softener is never completely regenerated. Based on the grains of hardness and number of people in the house, you adjust the demand meter. If it's just right, you'll never run out of soft water. I try to keep mine adjusted so I occasionally get hard water in the morning. If my shower smells like iron, I check to see if the softener regenerated overnight. If so, then I figure it's adjusted about right.
While you're at it, you might want to also install a reverse osmosis unit for drinking water. That will take out sodium that the softener added to the water, as well as arsenic and other nasty stuff that can get past the softener.