Sadly the mobile site on iOS doesn’t like to change tracks when the browser isn’t in the foreground. Currently playing tracks will continue to play when switching apps or if the device goes to sleep, but you’d have to wake the device or switch back to the browser every time a song ends (yuck). Interestingly even the built in iOS play/pause controls will work from the lockscreen. Google needs to give iOS some Music love for this to be useful for iPhone users.
OTOH, it seems you can’t even sign up for the All Access trial without signing up for Google Wallet, so it all becomes a bit moot for me anyway.