UsenetServer is owned by Highwinds, so you can expect the same retention and completion as Ngroups, Usenet-News, Newsdemon, Newshosting, and most other resellers out there.
One big difference. UsenetServer only lets you access the US server --not Highwinds' EU server-- so if a file is incomplete on UNS's server, there's no backup to go to.
About 3 years ago it seemed a lot of people left UNS because of major completion issues, as having no backup server can make a big difference when things go bad.
For an unlimited SSL account using Highwinds, I'd suggest Ngroups. It's also $10/month (when prepaid for 3 months) and they also have excellent support. And like all Highwinds resellers (except UNS) Ngroups has both a EU and US server.