The thing is that it is hard to tell what kind of groups they run and the level of activity. I am sure there are all kinds but is this a private or connected to other usenet groups as well?
If you go to the homepage, there's a link to the complete list of groups they carry There's also a search box to check for specific groups if you know the name.
Astraweb is a private company that provides individuals with access to Usenet news groups. AFAIK they are not connected with any specific Usenet group or affiliated with any other newsgroup provider.
Posting activity will vary depending on the group itself. Astraweb has no control or influence over that. But postings to active groups show up almost immediately on Astraweb's servers as far as I can determine. If I refresh the headers in my newsreader while I'm in a very active group, I'll almost always see several additional new posts each time I hit the button. And any time I've posted, I've seen my header show up in the group within a few minutes.
(Too bad Astraweb doesn't offer a free 14-day trial like Giganews.com