There is a small security/privacy issue that Unison users should know about. If you use more than one news server, it will check the groups you are subscribed to on any one server to all other servers you use, making those group names available to the curious. If you use NNTP for internal workgroup communications, you want to avoid this program for use both there and on public services.
Perhaps it's just a punctuation issue, but I'm not entirely clear on what this issue is.
If I understand you correctly, you are establishing a case that you have one set of newsgroup subscriptions on one usenet server, and a different (possibly overlapping) set on a different server. In this case, are you saying that the superset of all subscriptions on all servers will be checked on any given server? And are you also saying that, furthermore, any users who have access to your list of newsgroups on one specific server will actually see this superset list of newsgroups?
If so, I can understand how, for those who require usenet for their work environment, this could be compromising. A possible work around might be to have two separate installs of Unison, one for each server.
That said, I migrated to the Mac only recently. I was using virtualization to run a Windows newsreader that worked for me, which ultimately drove me to upgrade from my CD Mac Mini to a Mac Pro. Almost immediately thereafter I found Unison and I haven't even installed a virtual desktop on the Pro since rebuilding it.
I've got to say, Unison is about the cleanest, slickest little newsreader I've ever seen.
As to the cost - I guess I just don't mind paying someone for their hard work to develop a program that suits my needs. Freeware is great and all, but compared to the $1000 it costs for some professional applications, I can deal with $25...
Mike