Descaling system: useful or not?

We already live in the same drinking water supply area as our new building and have 14 dH. Yes, the limescale spots on the fittings are annoying, yes, descaling the appliances (e.g. coffee machines and kettles) is annoying. But we have decided against changing anything about the drinking water quality, we have decided against getting another device in the house that incurs purchase costs, requires space, salt storage space and time/money (refilling salt, keeping an eye on it, regenerating), etc. And the limescale does not go away, it can only not adhere as easily. Of course, you notice the difference. But we don’t have black fittings and no dH over 18, so we crossed that off. For us, finally, a lot of time and money would have been involved, but that was on the budget cut list...

Hmm time? You probably save at least one cleaning process per month (at least), so you can easily refill salt once in a while. Everything else is done automatically by the systems nowadays. You would have to calculate the money or find statistics on how often a dishwasher or washing machine is replaced with descaling vs without. But yes, the comfort is dispensable, especially if you don't even have hard water. 14dH would be the limit for me to say yes...

I was offered a Grünbeck softliq18 including 2x salt, installation, commissioning, and 1x Schuko flush-mounted socket (separate electrical circuit) for €3,900 by the developer. According to Idealo, the system is available for €1,680 in free sale, so the offer seems quite high to me. Alternatively, only the preparation for independent retrofitting later for €690. What is your opinion? Best regards

One is purely a curb edge, the other a ready-to-operate installation including 5 years builder warranty.
Of course there is a price difference because both the installer (rather modest) and the builder (rather more) want to make a profit.

Alternatively, just the preparation for independent later retrofitting for €690.

The mounting block already costs €400 on the open market, without installation and without installer + builder margin.

The assembly block already costs 400€ on the open market, without installation and without the installer’s + developer’s margin.

I’m not sure if we mean the same thing by "assembly block," but I consider the offer of 3900 EUR completely excessive.

The system itself is, as mentioned, around 1500 EUR, and "preparation" usually only means a power outlet + drain, which are heavily priced at 200-300 EUR.

In our case, we are lucky that the plumber (from the general contractor) himself offered that I should directly procure and place the system. Then he will connect it directly, which would be an additional effort of 15 minutes. The installation is still to come, but I assume that shouldn’t be a problem.

I bought the SD21 system with assembly block (!?) and all accessories for 1750 EUR.

Then you have a nice plumber. Many do not install products provided by the client because of the warranty and such.