I have to say I don't think it is their strength, they are ok, but not in the same category as their normal bats, which are fantastic, also they take even longer to play in, probably 18 months to 2 years. Further for me the best maker of butterfly willow bats is Paul Aldred, they are sublime, and I would say of the many butterfly willow bats I have had. His are head and shoulders above the rest, and somehow for such hard timber play well from the beginning.
Hope that helps.