[ENJI (Gen)] Mujikaku na Osananajimi to Kyoumi Honi de Yatte Mitara 3 | I Tried Getting Laid With My Oblivious Childhood Friend Just Out of Curiosity 3 [English] [Digital]
@snailord13 Presumably the original doujinshi are mosaic-censored, while the tankoubon has transparent bars instead.
As to why they did it that way, usually this kind of thing is some combination of 1) different regulations and standards and 2) offering an incentive to buy the tankoubon.