http://e55lzoju6enqswtvm66sk3uqukcin3377ehgiorplj4d7qyssipls4yd.onion/en/blog/what-is-a-bitcoin-mixer.php
As the name suggests, it requires that the user trusts the mixer to hold his or her money and the fact that the mixer knows who exactly sent and received the money, making it still a risk to keep in mind if one is really concerned about revealing their identity. Another disadvantage is the fact that the mixer could be a scam, essentially stealing the user's money.