It's okay for transactions but I would never leave a substantial amount in there. The IRS will get them eventually and shut them down just like the rest before them.
I love BTC, but you really want to assume the Feds can and will trace all your transactions if you're not careful. The idea that "tumblers" can essentially remove the breadcrumb trail is 100% false. Though it is difficult to trace, it can be done as the trail always exists. The best route to take if you're serious about BTC and/or would like to receive BTC in exchange for black market goods/services is to completely anonymize yourself; pay for and use clean proxies, VPN, and have nothing connecting your real persona to any BTC exchanges.
In all honesty, I'm just a person on the internet who can say anything, but I have setup and managed BTC services for various "providers" whom have stayed safe. Others who believed the whole anonymous BS have been caught. Protect your freedom at any cost!