it copies files from application dirrectory to local storage
Unfortunately this is required as the Air compiler incorrectly compresses embedded sound files, so the native Android code can't read it unless the file is uncompressed and moved out of the app bundle. If Adobe fixes this in the future we'd be happy to update the ANE.
I could take long time due to compresiing issues.
We've found the transfer time to be very quick. If you are worried about loading speed you should pre-load the sounds you need on a loading screen, just as you would do for image assets.
soundPool itself has vugs with loading performance
We're using this ANE in an app targeting Android 4.1 and higher and haven't had any issues or complaints. It may not be perfect for every situation, but it makes playing sound effects on Android easy.