I am using Unmixr since two months and i can say that this is the best tool for text-to-speech on appsumo. I am writing this review in context of indian accent of english, hindi & other regional languages. There is lot to improvise. My suggestion is to add template setting for stroy-telling, news, audiobook etc. so that the engine gives best results.

Cons i found is in UI, it lags sometimes, and sometimes it doesnt give output. Also, for some indian voices, there is background noise in the final audio, but it was gone after few regeneration. I am not sure of the reason.
Also, API is not yet available. This restricts any automation you want to do for clients. So, requesting unmixr team to work on this as well. All the best to Unmixr team for future development.