From a school perspective, a school chooses it because it...

From a school perspective, a school chooses it because it provides a very complete package, ie internet filtering as well as parental controls that interface with the internet filtering. As far as I know, no other provider does this, ie some do both but don't provide a package to the school. It also provides this package at a very affordable cost...infact its one of my sore points that they provide this package to schools much too cheaply.

For example, one of the biggest education online security providers in the US, iboss, is useless if child has no parental controls because it only applies to school network, not child's 3g/4g network. So if FZO approach a school and say look we'll give you our internet filter at a much cheaper price than iboss, and our parental controls for your students (either optional or compulsory to parents), it's a very tempting offer to the school. They get the security features and can cover their student cyber obligations more completely by offerring parental controls to the parents.

From a parent's perspective, I have no idea if its the 'best' or not as I have never used it, nor any others. But I have looked at reviews of others & FZO seems to beat them hands down in terms of features, especially 'at partner school' where the schools are using their Linewize internet filtering service which interfaces with kids that have FZO on their phone. I have also spoken to people that do use it, and swear by it. Its cost, assuming just direct, is competitive with the alternatives. But it can be FREE if people purchase a Woolworths mobile plan (WW pay FZO out of the monthly plan amount I believe), or if child is at a school that provides it for free.