Nothing wrong with being cautious.
You’ll actually find that torrent sites that require login information are far, far safer as far as copyright takedown notices go. They target people who pirate new MPAA and RIAA releases, and occasionally take down the extremely massive private ones, as they did with Oink about a decade ago.
As far as ‘download utility’ I assume you mean the torrent client software? There are dozens, if not hundreds of those, and that is indeed an area to pay attention to. As with any freeware app, the longer it’s around, the more likely the authors will sell out and begin bundling it with other useless garbage and adware. qbtorrent is clean and easy to use.
Not sure what the decryption ability function or corresponding concern is about.