No, I don't mind using their algorithms (I'm sure they are correct anyways). I just mind that I can't tinker the algorithm to be optimized for my special use case scenario.

You can have accuracy and scalability. It's just that normally you run these types of things in memory on one machine, not on tens to hundreds of thousands of machines. So these algorithms have to be decoupled and that isn't easily done (but I'm sure Google figured it out a long time ago).