If offer 2 from Interhyp is correct, go for it, those are extremely above-average conditions. I come to at best 2.24% with the numbers for a 20-year term, maybe he also calculated 15 years for you or a portion with the KfW with a shorter fixed interest period. Always have the total costs calculated until the end of the fixed interest period, then the comparison is not difficult.
That was the personal area where you could calculate your own conditions. As I have learned, it was a full repayment loan, although I had selected a fixed rate... unfortunately, their technology does not seem to be correct in this respect from the customer's point of view. Accordingly, the offer does not exist in this form, it almost seemed too good to be true.
I find the mix with building savings already quite interesting, but not quite as transparent as a classic annuity loan. Therefore, I am currently struggling with it. In my opinion, even calculating the costs is not quite so easy.