From past experience of having to dig out a wayward patch of some kind of Buddleia sold as 'Blue Chips,' (but didn't really look like other pics of plants by that name, so I never believed that's what it was,) I'd say to avoid the BB's that aren't sterile cultivars. (It had droopy, washed-out looking blooms.) If they're seedy, they're weedy, IME.
The well-behaved one I've kept moving around with me for the past 25 or so years is a wonderful plant that butterflies do love, no seeds.
