I dont have any HC devices, but I've used them in-store. I haven't ever noticed the buttons/bar disappearing in any apps, inc the browser.
It sounds like a recipe for disaster when you have to actuate a press to get the buttons to appear, especially if you accidentally hit something unwanted or more-often-than-not your empty trigger will automatically register an object close to it... because Android is like that sometimes.

It would be good if Samsung added the 5MP shooter from the original SGS and the phone radio frequencies and sold it for $199 instead. Still waiting for Galaxy Note or Galaxy Prime, here.