I'm a long-time Transmission user but I just learned that VPN killswitches are a thing (how did it take me so long!?). I would like to try another client which has this feature in case I forget to launch my VPN client before opening Transmission. Does anybody have any recommendations? Deluge? QBittorrent? Or any others?

UPDATE: Thanks for the suggestions everyone! I decided to give qbittorrent a try and have been enjoying it so far.

I followed these steps to bind it to my VPN from on Linux:

1. Pause torrents
2. Connect VPN
3. Open qBittorrent. Go to Preferences, and then Advanced tab
4. Change network interface to tun0. If unsure, disconnect VPN and restart qBittorrent then repeat step 1 to see which interface appears.
5. Restart qBittorrent
6. Test it out on the official kubuntu torrent or your favourite distro from LinuxTracker.org. Turn your VPN on and off while verifying whether it pauses and resumes downloading.