Loving these kind of apps :-) I personally use WhoBird, which runs complete local on your android device, so it works also when you don't have internet and is available on fdroid (https://f-droid.org/packages/org.woheller69.whobird/). Will give merlin a shot as well to see how it compares
AFAIK WhoBird uses the same model (or at least, also developed by Cornell), but for me, Merlin is still better at identifying multiple birds at once.
whoBird is only working with audio (and not photos) though
Merlin also works offline. I use it all the time out in the mountains.