Hi,
I knew about this for some time already but their website was down. It’s up again 
So you can look it up there: https://www.voxygen-group.com/.
They have a lot of different voices and languages for TTS. See https://www.voxygen-group.com/content/voice-language-catalog. From what I tried, we can definitely hear little glitches that show it’s a computer-generated voice, yet I like how it does various accents. For instance the various UK voices all have different accents. It’s easy to test by yourself directly on the website.
They don’t support arm on Linux but they do support arm on Android and separately x86 on Linux, so I bet it would be easy for them to generate a arm/linux port.
For STT they support french, american english and UK English. They have a Cloud service that can be either used as SaaS or installed on our servers – does that mean this could be installed in the box? LIkely not, I guess this needs more cpu.
Note: This startup was initially spawned out of Orange Labs, so maybe Fabrice knows some of them