I have found
They utilize ERC-20 to ERC-721 conversion within their contract by assigning each id a value. Our approach doesn’t separate NFTs from tokens and instead couples the transactions together. Always using both token standards in a transaction (unless the user has more tokens than IDs, transfer less than 1.0 tokens, or don’t roll over or under a balance of 1.0 * n tokens). Each ID is equivalent to 1.000… tokens making it so that any user whom collects 1.0 * n tokens will receive n NFTs with no need for further conversion.
and
DN404 is a separate, unique, approach which links 2 tokens together. This creates the requirement of handling 2 tokens addresses (one for ERC-20 and one for ERC-721). Our solution only requires one contract, making usage streamlined for users by them not needing to track 2 addresses. They also implement a way for users to skip minting and transfer of IDs. We offer a similar solution. However, we only allow the skip of minting to ensure parity between user balances and ID count.
It also may be worth noting that Emeralds predates all recent hybrid token implementations with our Emeralds v1 which was sadly a flawed implementation which we improved on after an exploit.