As far as slowing down the internet is concerned, my experience is that it depends on how you use K9. It was designed (I imagine) with the idea that a few categories would be blocked, and say 90% open. So when you try to access any given website, it only needs to check that website against 10% of their blacklist. This is fairly quick.
However if you try to use k9 to block almost anything then it goes very slowly, as it has to check almost every category.
When I went to TAG to ask that they install k9 for me, I specifically asked them not to block categories like smoking. That category is for smoking addicts, there is no reason whatsoever why your standard frum Jew would want to block this. There are quite a lot of categories like this. I respect TAGs mentality of Ossur unless proven Mutar/necessary, but this is what slows down TAG in my experience.