They're good but....
I have used them and they're not bad at all, but their retention on some of the binary groups is pretty limited. Cheaper than easynews and giganews tho.
Here's the cheapest I've come up with, their retention is better than clara too:
usenetserver.com
If you're using grabbit, you'll be interested to know that clara allow 3 simultaneous connections and usenetserver 6!
Hope this helps.