I think it's a personal preference thing. I've only really done karting, and for me, the helmet does not really obscure your view, so I don't like my view blocked too much in games. However they do give you a false sense that you have more peripheral vision sideways than vertically (i.e more widescreen feel). The problem with the camera in the helmet is that you need a really good fisheye lens.
Personally, I would only like to see half the visor strip at the top, and a very little bit of the trim on the bottom, without blocking the view to the steering wheel.