What happens if I have multiple Death's Dances?

So I've been trying to test this out in a few custom games but can't seem to tell if its actually reducing more dmg and healing more if I have multiple Dances... Has anyone tried this out and seen a conclusive result? Just asking because having 4 of them would give you 40% cdr, and 50% dmg reduction with theoretically 50% lifesteal as well... But yeah... I can't seem to get a good read on it to see if the passives are stacking or not. They're not named passives which makes me think they should be able to... anyone else try this?