The downside with those is that the build of JavaScriptCore is significantly bigger than the one React Native currently ships with. It's quite a big dependency to have in an app, and a shame Google doesn't expose the system V8 runtime on Android in the same way Apple does with JavaScriptCore on iOS.
Android stopped having a system V8 runtime several years ago. Ever since all webviews you use are just frames to a normal app that's updated over the normal app stores.
