TA loan with building saver - read a lot, yet did not find the catch.

But if you factor in that you will be finished 3 years earlier with the grants, you have 3 years to save money in order to pay back the 16k with a 30% discount in one lump sum.

It wouldn't have been 3 years, but I agree with you, Riester would not have been a disadvantage.

You have to be careful with Riester, there is more involved... for example, you are not allowed to rent out or sell the property (or in that case you must purchase a new one within two years). Otherwise, you have to pay back the subsidies. I had a Riester pension, and I have now withdrawn the saved capital. It involves bureaucracy again, with the ZfA, then it costs commission or distribution fees every year (!) with the contract partner... it sounds great to take advantage of the subsidies, but actually only part of it arrives and you have a lot more paperwork and additional restrictions, see above. I am no longer convinced. (The housing promotion account is not debt, you have to pay tax on the value upon retirement.)

I have to admit that I am not a fan of TA loans. For me, it's not just about the interest rate and what I save, but also all the other conditions. Something stupid has to happen in the 5-10-14 year range where you are forced to sell, and you have practically paid off nothing and only paid interest.

Such a TA loan is even more of a bet on a positive and problem-free repayment over the decades than a pure home savings contract. No, that would not be for me!

€334,000 loan is financed at 1.19% effective interest over 15 years.
Simultaneously, a building savings contract with Wüstenrot is concluded with 1.25% nominal interest rate (1.82% effective) during the repayment phase.

Please also check whether the installment suddenly increases in the repayment phase; otherwise, this is a comparison of apples and oranges. Furthermore, a building savings contract plays out its advantages over the term.
With every special repayment, any potential advantage compared to a classic annuity loan becomes smaller. Especially when you are just at the beginning of your career ladder, you should consider this.
We built 5 years ago; back then, we had a theoretical term of over 30 years (without special repayments). However, our rate was designed so that we could live with the rate even in cases of disability insurance or unemployment benefits. It was thus clear that special repayments would come, only the amount was unclear.
Due to major salary increases, it is now very likely that we can repay the loan in 15 years. A building savings contract would therefore have been completely pointless.

We were advised against a building savings contract because the payout is not guaranteed. Only the amount paid in over, for example, 15 years. Calculate a classic annuity loan with, for example, 20 or 25 years fixed interest rate. You also have the option of special termination rights after 10 years or later if the interest rate continues to fall.