I was looking at those helmets a while back. My opinion is you would get used to it and I think it could help in making motorcycling safer. I would need to test one out for a few months to confirm this obviously.
The trouble is today I think you do have to be aware as much as possible of what's going on all-round you, and that does include what's behind you. I thought the price was realistic, as originally this type of technology was going to cost a lot more. Note the rear view part you look in is adjustable.
Here's the link I saved, there's a video in it worth watching:-
http://www.reevu.rapidbikes.co.uk/rear-view-helmets.php
Chris.