It was an extremely vigorous self-seeder in my garden. If you are quite diligent at deadheading, it would most likely be fine, but I planted a plant one year, and had 25 plants the next year, and removed both the original and all the seedlings that year, and then continued to remove seedlings for the next 5 or so years. YMMV

I would not call it invasive because I don't think it changes the habitat radically or makes it inhospitable to native species. However, It is an very enthusiastic seeder. Just like NHB one plant produced dozens of seedlings. If you don't mind pulling them, the smell of the flowers is very sweet and the plant itself gets quite tall early in the season which can be a feature in the garden

Thanks for the input. I'm going to let my self-sprouter be for now. It's not in the garden, but in the pachysandra along the driveway, out of the way. I'll let it do what it wants, hopefully multiply a little there (which I would assume isn't easy to do among pachysandra) and it will be there in the future if I need it. Thanks for the information!