"There are many reasons to not consider open source NAC, the
first of which is how much workload do you want to put into your
NAC solution, above and beyond having to figure out what you want
your NAC to do for you, lay out policies, ensure your network
architecture will support NAC, deploying the product, managing
end-points, and a bunch of other little things that in totality add
to your workload.
"If you work for a university where you have a large pool of
talented, but cheap, labor (interns), then an open source project
might make sense because you have people who can manage and
maintain the system..."