Make a special repayment or pay off the KfW loan?

Interest rate difference between bank loans and Kfw is marginal, therefore repay Kfw.

Then the sentence must be wrong.

The only disadvantage I see is that you park the special repayment in a daily allowance account. In 5 years the car breaks down and you use this saved money to buy a new one.

I always say " what’s gone is gone"

Better to take out a home savings contract for the outstanding debt and/or ask KfW if the repayment can’t be set higher here.

That is of course difficult, since an exact savings rate probably cannot be defined. In the end, he does not get the home savings contract ready for allocation.

Sorry then I don’t understand your sentences or only to a limited extent.

On the one hand, you warn against putting the money into a daily allowance account, on the other hand, you advise paying off the KFW. Only the explanation with the building society savings contract could somewhat reconcile both.
That is of course difficult, as one probably cannot define an exact savings rate. In the end, he does not get the building society savings contract allocated.