Avoid them, you must trust the mixers because, in order to do the mixes, you have to give them your bitcoin!
Better you use the Coinjoin technology and the best implementation in my opinion is JoinMarket even if it is not the easiest one:
https://github.com/JoinMarket-Org/joinmarket-clientserver
Other solutions can be Wasabi and Whirlpool but I do not recommended them for different reasons.