I can't use Deluge b/c I need a torrent application that can be tied directly to a network interface. (VPN interface).

Qbittorent has a setting where you can tie to to the interface. If the interface loses connection, then it just ceases to work.

This function of Qbittorent works better than any VPN kill switch, and IMHO it's a killer feature that's worth the headache.

Also, Deluge's (and other's) web interface are usually good for adding/removing torrents - but usually are pretty awful at allowing me to specify download location, or using the torrent application to change torrent download applicaiton, nevermind label management and so forth.