A tip...
The best results may be achieved through tweaking the filtered words a bit. Quite a lot of the internet disappears without doing so. For smaller children that's not much of a problem, but teens expect a bit more latitude. Even words like "prostituted" are prohibited. I found out that my own blog was blocked - and I run a pretty sparkling clean site. So one may have to add a bit of "real-life" to the filter.
Yes, the software isn't completely invisible, for tech savvy teens anyway, but it has lots of features I like - like shutting down the internet after a certain time on school nights.
;-)