This might work well in android where if one app (maps) hands over control to another (third party public transit info) -- the global back button will take you back to the first application when needed.
iOS always seemed to be designed with monolithic apps that did everything and hence not require too much app switching to complete a certain task. (at least on the iPhone. On the iPad the four finger swipe makes this a moot point)
But what iOS needs is for google to provide a replacement maps app and to register itself as the default maps handler (in effect stop the built in and useless-at-this-point-to-me maps application from ever launching)
I guess I'll hold off judgement until I actually use it.