The Helix process uses a new proprietary technology which has never been used before with bitcoin tumbling. The coins are not just mixed but traded out for new ones before mixing. By trading dirty coins for out for new coins helix severs the taint trail.
After the intial transaction you send to Helix has 3 confirmations, the coins will be cleaned and sent back to you with 1 transaction immediately. The process can take up to 2 hours, but because of reserve clean coins, 95% of all helixes are sent with in 30 minutes.
The Helix system has a flat 3% fee. It is on the high end of the fee spectrum for bitcoin tumblers for a good reason. This system has lots of fees involved with many transactions to and from the exchanges.