The download speed on any popular release will max out even the fastest connections. I assume the retention for less popular content is a lot better on trackers, but I don't have enough experience with usenet to say that for sure.
security features
What features?
Torrents can be encrypted as well, and there isn't a need for a VPN unless you use public trackers, which I don't recommend.
What is the monthly fee for Usenet? I'm more in favor of decentralized systems with the use of seedboxes to speed up distribution, but I'm not against usenet either.