I don't grow these plants so have no advice. That Midnight's Child would look nice in front of a light colored or variegated plant so the blooms stand out.

Did you ever end up ordering from Opus? How was your plants?

I am a fan of Sanguisorba. I grow 'Tanna", tenuifolia, obtusa and obtusa alba.
These var. have been in the ground nearly 10 years with no issues. (tenuifolia will seed about if not deadheaded)
I have just planted 'Pink Tanna' in the fall.
They are intolerant of dry soils but if too moist will flop. obtusa is pink but will turn white if the soil is too wet.
I really like them all but 'Tanna' and obtusa alba are the ones I like best. I am sure I will like 'Pink Tanna' as well.
Red Thunder sounds quite nice. Could not find the height of Midnight's Child but it looks nice as well.
They have gone to town on seed selection / hybridizing. Wow
Edited to add
Hope arbo_retum shows up, this will teach me to check the OP date.

This post was edited by Peren.all on Sat, Jan 3, 15 at 18:43

There is a good article on Sanguisorba in the journal The Plantsman (published by the Royal Horticultural Society).

J. Sutton, "Sanguisorba in Cultivation". The Plantsman 6 (2) 2007, 78-83.

Unfortunately I can't find this article anywhere online (it used to be on the RHS website).

I did have Sanguisorba hakusanensis in my garden for some years but got tired of because it flopped. Now I have Sanguisorba "Pink Brushes" which SEEMS to me a more sturdy plant than S. hakusanensis. Love the fluffy flowers!