This is amazing! If you are looking for US EN and use a phone with arm64 I can recommend sherpa-onnx-1.10.27-arm64-v8a-en-tts-vits-piper-en_US-kristin-medium and sherpa-onnx-1.10.27-arm64-v8a-en-tts-vits-piper-en_US-norman-medium.
Edit: I don't seem to be able to get the engine to show up as a tts engine but it works well within the tts app itself. Hopefully I'll find a fix I've been searching for a good tts engine for android eBook apps.
Edit 2. Fixed I mistakenly downloaded the standalone version from https://k2-fsa.github.io/sherpa/onnx/tts/apk.html instead of https://k2-fsa.github.io/sherpa/onnx/tts/apk-engine.html
Yeah IMO they need an app that can download/manage models directly