Sure but here in the UK schools will use what is cheapest, free or part of a wider package of software already used. RM web filtering or smoothwall make me want to bash my skull against a wall at times. Finally School IT staff are not judged on their ability to manage a web filter well. Safeguarding is (rightly) the primary concern and so if an existing solution can be said to block the more egregious parts of the internet, it's irrelevant if it blocks the useful parts too.