How does it compare to Appcelerator Titanium? That's also a JavaScript-to-native-UI layer utilizing a JS runtime. http://www.appcelerator.com/titanium/
I know one complaint among many was that wrapping native API in a new framework can limit access to functionality and customization; you're limited to the choices of the framework designer. Another is debugging is harder since native tools don't understand the framework and you're dependent on the tool chain provided by the framework makers.
That’s why they (Appcelerator) have a pretty solid but not well documented plugin infrastructure.
At the same time they are moving to a more native-friendly infrastructure, code-named Hyperloop.
I know one complaint among many was that wrapping native API in a new framework can limit access to functionality and customization; you're limited to the choices of the framework designer. Another is debugging is harder since native tools don't understand the framework and you're dependent on the tool chain provided by the framework makers.