http://phandroid.com/2013/11/14/how-to-install-google-experience-launcher-with-ok-google-command/
The site seemed legit but when I went to the download mirrors it started asking me for credit card details and that is a BIG NO NO for me, especially when they say its all free and the wont charge.
thx
Sideloading by itself is not recommended, that means installing apps outside of proper channels where Google have no control over so you can potentially install malicious codes to your device. Although Android is very secure, it gives end users the choice. If you have Google PlayStore installed on your Android phone, it will scan sideloaded apps for virus and warn you if it detects any.
Android OS is free for endusers to use (except apps that required purchased from the developers and redistribution of Google proprietary apps that needs licensing if you are a manufacturer), so you should not have to pay anyone to use apps official from Google.
The Google Home launcher is available for the Nexus 5 only. You can either download the Nexus 5 official firmware and decrypt the system.img to get it, or download it from here:
How To Try The Google Experience Launcher With Translucent Bars And Google Now Once You Get Your KitKat Update [APK Download]
Also just a side note, everyone likes to call it Google Experience Launcher, but Google had never officially called it that, some tech website made that up. This launcher app is really just a plugin for Google Search, which is the real backend of the launcher itself.
Is this process legit? will it compromise future download of KIT KAT?
If you don't root your phone you should receive future OTA updates. (You will receive OTAs with root too, just that you'll run into issues when applying the updates like bricking the phone.)