I’ve been using Web Books Viewer for a while now on both desktop and mobile. To answer your question, it does work offline on Android without needing the Chrome browser installed, which is great. I’ve had no problems with accessing my EPUBs or WEBZ files offline. The only thing I’ve noticed is that some features like bookmarking and annotations aren’t as robust offline – they stay on the device, but you can’t really sync them across devices if you go offline. It’s not a dealbreaker for me, but just something to keep in mind. Still, for reading, it’s definitely a solid choice!