One big distinction. Most of the NT packages are just that: finished
packages that you can use with a variety of networks. You can set up a UNIX
server that will packet filter, then you simply have to find the list of
200,000 sites that you want to ban.
I expect to pay for services but am to somewhat chagrinned at the costs.
Regarding $1-$2 / person / month.... that is what I would like to be making
if I made such software.