With Vuze Plus you also don't have to wait for downloads to finish because it will stream torrents as they download to your computer.
No chance of uploading files for the public to their server? There are plenty of legitimate, non-pirated files, such as movies without copyright protection, open-source programs, indie music, and much more that it can be used for.
Questions about legality are purely content-related, having nothing to do with the BitTorrent client or protocol.
The application is free, although there is a chargeable version which includes anti-virus, file conversion, secure access.
Extratorrent has more than 1 Millions torrent database list, this is massive.
However, the site is pretty well-established and is nearly half a decade old hence the chances of it spreading viruses or malware are pretty negligible.