Ive actually never used the code but looking at your example I see a potentially nasty 'bug' in its implementation.
That being that all code within that frame and the frame of the label checked will be run as the playhead does pass through those frames (even if not reflected on screen, the script in those frames are run).
So, if isAtLabel is called within the frame, it checkes the label, if different, goes to that frame, then returns to the currentframe which would then re-call the that frames script, which if containing the isAtLabel function call repeats the process in an infinite loop.
I put a warning at proto
though I dont think there's much in the way of getting around that based on this method of interpreting a frame label match.