So you're paying 0.0013 BTC but 0.0010 BTC has to be sent back for mixing? Does the participant then get the 0.0010 BTC again after mixing?
4.9% fee is outrageous, that's my free honest review for you.
Most I have calculated are around 5% + 0.0007 BTC
A small saving is significant when distributed across a large number of transactions using the service regularly.