My 'Bluebird' was 10 ft. by 10 ft. before I mostly cut it to the ground, last Winter. I hoped it would come back, and, being easy, it has. It will bloom soon. I concientiously pull up any seedlings, even though they must be just from my bush. There are none other nearby except a new, small, 'Blue Satin', that waited until it was 4 feet tall to bloom. Any seedlings would probably be close in appearance to the parent plant, but you can never be sure.
I do prefer the appearance of the flowers on 'Blue Satin' although neither are really more than a violet blue.