Is there any other alternatives, how can you be certain anonymity?
There is no way to be sure 100% unless you build it on your own. Even though the code is open source, let's say, the owner could simply use another code or log everything on their servers. If you look for 100% anonymity, then you should do anything on your own. Make your own Mixer, use tor etc.
What a practical solution,eh? If there are Mixer owners here we would really be glad to hear out their words about anonymity.If we do make use of mixers then we cant really be sure if its 100% anonymous.