I find this technology to be very scary. As indicated in the article, there's no reason that it would be limited to being able to determine only what you've seen. It could easily be extended to determine what you're thinking about.
For one thing, it turns protection against self-incrimination on its head: If you don't subject yourself to a brain scan, your guilt is presumed. If you DO, you're essentially testifying against yourself.
And there are many, many other problems. For example:
Suppose you think unflattering thoughts about someone (your wife, your boss, a relative), but it's not something you would ever actually say out loud.
Or suppose you engage in kinky sexual fantasies for pleasure, with perhaps some of the "action" illegal, but not anything you really intend to do.
Or suppose you merely THINK about actually breaking the law in some way, but ultimately decide against it.
In our present world, none of the above thoughts would "count" against you. You remain a loving husband, a loyal employee, a favorite nephew, a morally-upright citizen. But can you imagine a world in which the fact that someone could ask you - to "prove" your worthiness - to subject yourself to a brain scan that could determine all your private thoughts?
I think it's a terrifying prospect.