Yeah but this has 2 Limited Editions instead of one for Zassou no Uta and you can't say ZNU was better since both are totally different styles... I think the sales are affected by how people look at Buono!'s image which is really sad..
Two PVs helped ZnU a lot. Berryz went from 30k+ to 20k+ when they stopped the double a-side thing. And Natsu Dakara is infinitely better than Zassou no Uta