Our school doesn't allow access onto the network without McAfee Spyware&AV + SiteAdvisor installed. NAC is the safest and easiest implementation of making sure the students are fully protected.
AV/Spyware for all those baddies.
Siteadvisor/Squid for all those web requests, theres nothing illicit or illegal they can do, and thats what we want for a boarding school.
And the benefit of McAfee it runs on all OS, just different engines. We do have quite a few Mac users and quite a few Linux users