This appears to be a repackaging of RealTimeVoiceCloning [1], albeit with a few additions, such as GSTs.
No matter what the repo claims, your results will depend on high quality data. Lots of it, and with ample fine tuning. Demo videos are absolutely cherry picked.
If you're picking this up for a project, HiFi-Gan is pretty much the best vocoder right now. Tacotron still produces great results, though there are lots of other interesting model architectures.