In the current situation with generally low interest rates a Bausparvertrag doesn't provide much advantage to regular mortgages. What you could do with it is to secure low interest rates for the time when your regular fixed interest mortgage is over. Example: A colleague is now building his house and got a regular mortgage with fixed interest for 15 years. Additionally he made a Bausparvertrag with a low interest rate, which he will use after the 15 years to pay the first mortgage contract off and then have another low interest mortgage independent of the general situation then.

But one thing i would definitely keep in mind if i were you: I guess your family friend just recommended a Bausparvertrag to you, because incidentally he could arrange a contract (and of course get the arrangement fee), and not because it's the best product for you.