But isn’t it would be like full of viruses?

Not any more than the websites the search plugins use. Its basically searching the same way you do, on the sites you specify.

The search lists are community compiled and maintained and use dozens of those sites. Of course don’t completely trust it… but it works really really well…

Qbittorrent search plugins

The biggest benefit is you can search everything so you don’t have to trawl multiple sites. You can also add private trackers to it as well.