That's pretty smart, but if you are using both mixers then don't you have to pay the fees on each one separately ? so fees will rack up?
Yes. In the example of the picture: 2,5% + 0,0007 BTC + 2,6% + 0.0005 BTC in fees.
If you mix 1 BTC with those settings, you receive 0,9498318 BTC.
Maybe you could add an option to calculate the total fees (and how much you will receive for what you send) when using both mixers.