d) Most importantly is that in Zcoin, total supply is still visible so if there's a flaw and someone is secretly creating coins for themselves, this can be much more easily detected. With Zcash, if a flaw is exploited, it may be almost impossible to detect as someone can mint coins for themselves without being detected.
Yes, it was so easily detected that someone (hacker or inside job?) was minting coins for himself for weeks and almost doubled all the coins in existence before it was fixed.
https://zcoin.io/language/en/important-announcement-zerocoin-implementation-bug/First those who bought Zerovert got shafted and now those who bought Zerocoin got shafted. Time for a new project once again?