Jason, your article relates to H. perforatum which is also known as common St. John's wort. I have previously grown St. John's wort in my garden here in the PNW, did not find it overly aggressive, and have successfully removed it during a yard renovation when it no longer fit in. I didn't have any problem with it reseeding, and it actually spread out slower than I had anticipated. Perhaps that one was a hybrid of some sort - that was back before I was actively tracking the latin names of my plants.
In any event, the variety I purchased is a more compact hybrid which is not as aggressive as the common form. Perhaps it is sterile (like many butterfly bushes offered in Washington), although I haven't found a lot of information online about my particular plant. I am planting it in the medicinal section of my herb garden and plan to keep it confined to about a 4x2 foot area. Since I know it will spread by itself I only bought one plant which looks a bit silly at the moment, so I'm trying to get a couple more starts from my existing plant to fill in the target area quicker.