Single vs. House Softener
I've said it before, and I'll say it again, a dishwasher that softens its own water is still liable for hard water damage, mainly the valves that control the flow of water BEFORE it reaches the ion-exchange resins to be softened.
There are also extra wear and tear parts, such as brine pumps, diverter valves (water) and the softening system itself - which can wear out in under 10 years (resin lasts around 10 years MAX on city water - as chlorine causes the disintegration of resins) - all of which could make your experience wooful, if the machine chooses to be unreliable.
If I were you, I would invest in a house softener, or one of those magnetic things (if you are willing to spend money on something that basically may not even work) - which is a far better option than the machine softening its own - since you get 100% protection for each water bearing appliance in the home, less soap usage, easier cleaning AND your dishwasher doesn't have all that BS to go wrong. Not that it will, and I don't think anyone here has had trouble with dishwashers that soften their own water, but you should question how economical it is to run a full softener for everything, or just a little one built into the dishwasher.
I can honestly say, at 25 grains per gallon hardness here, you'd be silly not to have a softener. But a lot of Australians don't even know what "hard water" is - but they notice their kettle dies every 6 months (YES! This is true - even with frequent cleaning!). Do you really want to shower in that, or let your fancy front loader have a "wiff" of that stuff? NO! Please, take my advice. You will do yourself and all your appliances a big favour in doing so
