I can attest that Air 3.0 works so frickin great on my Firesticks.
I ALWAYS download any apk's from reputable known sites, BUT then process each and every APK through virustotal where 50+ malware engines scan for any malware items. NO exceptions! Once passed; I send them to Downloader on the stick and then install the verified clean apk. Really easy stuff. I don't ever use the amazon app store even if the app is available there because I want the verification and control.