You're saying they're imposters but I wouldn't say mixers are scams or say they're imposters of coinjoin services. They're providing a service which isn't coinjoin it's different obfuscating in different ways. Coinjoin's the best way to mix but it doesn't mean mixers aren't offering a service.
Mixers are scams that are imposters of coinjoin services. They do not provide any privacy, they simply allow the operator to steal your coins.
The mixing service you advertise literally takes user deposits and registers them for zkSNACKs' WabiSabi coinjoins:
UniJoin is a simple and effective solution for making your cryptocurrency funds like Bitcoin anonymous. Our crypto mixing service breaks the connection between your identity and your wallet address using CoinJoin. This is an important step to keep your anonymity intact while making transactions.
The key differences are they charge a 3x-10x+ premium on the fees zkSNACK's charges and, most importantly, they don't actually provide any privacy because they have full knowledge of all incoming and outgoing transactions they coinjoin for their users. If users simply coinjoined their funds directly instead of trusting Unijoin who coinjoins their funds anyway, they would actually gain privacy and also save fees.