For what it's worth ... secure multiparty computation requires a trusted setup.

Unless I'm a party in the multiparty (or you are, too), why anyone would trust a trusted setup is beyond me. Note that there is no indication that the secure multiparty computation was compromised and currently there is no auditing mechanism to find out!

Ring signatures, on the other hand, suffer from sybil attacks in that a malicious actor could try to make available his public keys to be included in the signature.

That said ... just because people (speculators) don't understand the intricacies of a particular technology, i.e. the mathematics, doesn't always imply that the token is not a good investment vehicle.

Finding out in detail how much a dev understands this technical background is always a good start.

Then again ... I tend to invest tokens based on utility, application, and, foremost, technical prowess and innovation.

ZCoin is most definitely on the list.