I don't think they do repeat flower. mind you I don't dead head mine as I leave them so that the flower heads get the frost and the birds can eat any seeds.

Mine aren't in flower yet,but they never repeat flower..I don't deadhead mine either, for the same reason as Sbg..
They are attractive to look at in the winter..I do however,split them every year,or they would take over !

I'm so glad I read the answers to this question because I have been deadheading mine and won't anymore.

They can be quite attractive in dried flower arrangements as well.