You should definitely avoid them if you have clean Bitcoins. There are two reasons for that. First is they are very expensive.
You will get much less out than you put in.
You will get much less out than you put in.
Thist is a pure exaggeration, I wouldn't call the fees that Chipmixer charges expensive:
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We use Pay what you want as pricing strategy. It mean you set how much value our service is to you.
Is Pay what you want too expensive for you?
Second is you might end up with Bitcoins someone pay to hire a murder with.
Common, not this BS!
There are also chances that you buy a used smartphone over ebay that belonged to Osama bin Laden. (we all know he is not really dead)