Compared to the memory footprint of web browsers, a Java BT app is pretty tame on modern computers these days. Nor do you have to faff around with installing JRE manually. It just works.
Resource usage is pretty good tho and it can handle hundreds of torrents with ease.
Yea qBittorrent, chosen as was meant to be lightweight so runs in a docker container on a Raspberry Pi 4 (but often eats all 8GB available RAM - could be just a problem with the docker imagine tho.) Haven't used Transmission so can't compare.