* How's the battery usage?
Exactly the same as GEL.
* I don't get "Say "Ok Google"" in the search bar, only a filled mic?
The hint is only shown for a few times when you first use Google Search, it's hidden after a while.
* Does this work with all languages?
No idea, if it doesn't work with GEL, it won't work here, however.
* Any other hotwords besides Ok Google?
No, since this uses Google Search's built in service, only Ok Google is supported. For other uses, consider OpenMic.
* Why is this only on KitKat?
The Google Search recognition service only works on KitKat.
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