Not OP but: they are apps to schedule automatic downloads. Like Star Trek Strange New Worlds but don't wanna go every week and download it manually? Set it up in Sonarr and when you wake up the new episodes are waiting for you. Radarr is the same for film, prowlarr for aggregating torrent trackers all in 1 spot, bazarr for subtitles, and there's a few others. Can also be set up with usenet in addition to torrents.
Yeah I switched after Jackett kept having issues with RARBG before they shut down. The biggest change is the fact that adding a tracker to Prowlarr will automatically add it to radarr, sonarr, and the like rather than having to duplicate everything manually yourself.
Sonarr and radarr manage downloads for TV and movies in a nice way for Usenet and actually torrents as well. You can set up quality profiles and choose which shows and movies you want to download and they will grab torrents/nzbs that meet your preferences, automatically start them in your torrent app or Usenet downloader, and then organize them in folders with appropriate metadata for Kodi/Plex when the downloads complete. They automate the process very nicely.
Edit, I'm a Usenet guy if that wasn't already clear lol
How is Usenet for privacy compared to torrents, e.g. if a usenet service you are paying for is compromised at some stage are they likely to be able to identify you based on payment data for example?