1- In Private Send, three users add their coins together in one big transaction, that sends the coins to freshly generated addresses belonging to the same three users. Like any CoinJoin solution, Private Send does require someone to construct the CoinJoin transaction. PrivateSend conceals the partipants’s address.
2- It’s not required that someone constructs the transaction. It’s done automatically by the masternodes.
3- Dash users must trust the masternodes with their privacy. After all, the mixing masternodes can link the sending and receiving addresses together; they know exactly which coins are going where.
4- ZeroLink framework, implemented in the Wasabi Wallet, the mixer is in this case unable to link the sending and receiving addresses. Clever cryptography helps break the link, without needing to trust anyone.