I have been seeing this bitcoin mixer advert here like chipmixer and bestmixer but I did not know what stand for. However, from your explanation I now know what bitcoin mixer is and that is like hidden identity.
With mixer, you can remove the traceability from your known bitcoin address.
Bestmixer is seized by the authority and I have updated it in the OP, you probably have missed that. Other one, bitblender has stopped its operation.