* Licensing (MIT)
* Quality (judge for yourself: https://rhasspy.github.io/larynx/)
* Speed (faster than real-time on amd64/aarch64)
* Voices/language support (9 languages, 50 voices)
I'm working now on integrating Larynx with speech-dispatcher/Orca. The next version of Larynx will also support a subset of SSML :)