Tor version should be top priority.

I don't trust clearnet any bit when it comes to mixing Bitcoins. This is how mixers get taken down or get spied on by Governments for months.

Obviously though their FAQs are not clear about fees, but they are displayed in the mixing page

They only display a minimum of 0.002 BTC in the sending address page, No idea about the maximum. I Wonder it they would mix 100,000 BTC at once