Oh, no fear of them becoming invasive here! I do get a lot of I. purpurea volunteers, but they're easily manageable. Anyway, I have a nice new south-facing wall with nothing growing there.
Think I'll give them a try next year in that spot. And it's right next to my also new french doors, so I can keep an eye on them if them bloom.
Looks like I'll need to look for trellises on sale.