Of course, fees always apply, and anyone who informs themselves fairly independently knows that almost the entire Riester subsidy is eaten up by the expensive products.
I mainly wanted to make one point:
If you haven't started the BV yet, there is a high chance that many boundary conditions will still change.
If you take out a building savings contract over 100k, then 1,000€ is already gone.
With a bank savings plan, if after 3 years you decide against Riester, you only have a few € in lost interest and perhaps 50€ for the premium-damaging cancellation.
Therefore, my recommendation would be to only take out a building savings contract if you are 99% sure you want to build soon.