what products are compatible with the CommonUpdater2 sites?
I don't have a complete list, but pretty much any product since VSE 8.7i will use CommonUpdater2 for content updates.
Regarding the content itself, next generation VSE will be using different content (but am pretty sure it'll still be hosted on that site). The newer content is much smaller, leveraging a new technology for scanning (AMCore).
If you go poking around the site you can see AMCore has content out there already for various products using that tech.
I am now using commonupdater2 as the source for my mirror tasks. My VSE 8.8 P4 clients seem happy, I am happy to save bandwidth and hard drive space.