The popular BitMixer.io is a selective scam. We tested this mixer with various amounts under 1 BTC and four out of five times it worked (once the funds just disappeared). When we tested with 2.17 BTC they simply stole the Bitcoins. No support or reply. Due to all the negative reviews, we conclude this is a SCAM.
Additional negative reviews can be found here: BitMixer.io SCAM