We use a FloPur Mark 8000. You can see it here
Flow Pur: Mark 8000
It works well. It has a 8000 grain capacity which means it will soften (for example) 400 gallons of 20 grain per gallon water.
We use about 13 gallons of water per day so we would have to regenerate about once a month.
Here in AZ the water hardness is 50 grains per gallon so we have to regenerate about every 12 days.
Note that some units like the Waterstick have a much lower capacity (1500 grains) and where the water is hard will have to be regenerated much more often.