I used a similar product on my wife's old 5 series.
It was old and had reached 165K - the car not the wife
Anyway, it did initially solve the loss of coolant into the pots and I ran it for a further 9 months before the symptons returned (loss of water and masses of steam being exhausted out).
My only reason for using it was that we wasnt ready to get rid of the car and didnt want to spend loads on having a repair.
So it served it's purpose, and yes I did highlight the problem to the chap who bought it from me. He was a mechanic and didnt even flinch at it. In fact I think that was the reason he bought it - buy it cheap, fix it and sell it on with a profit.
Hence, I think these products do have a purpose, but not for a long term reliable fix.
5 series, best car I've ever owned.