I use Piper for one of my apps. It runs on CPU and doesn't require a GPU. It will run well on a raspberry pi. I found a couple of permissively licensed voices that could handle technical terms without garbling them.
However, it is unmaintained and the Apple Silicon build is broken.
My app also uses whisper.cpp. It runs in real time on Apple Sillicon or on modern fast CPUs like AMD's gaming CPUs.
I had already suspected that I hadn't found all the possibilities regarding Tortoise TTS, Coqui, Piper, etc. It is sometimes difficult to determine how good a TTS framework really is.
Do you possibly have links to the voices you found?
However, it is unmaintained and the Apple Silicon build is broken.
My app also uses whisper.cpp. It runs in real time on Apple Sillicon or on modern fast CPUs like AMD's gaming CPUs.