The advantage of the two piece (separate dp and rp) is that it is easier to intall, not any more likely to leak, given the way that the TurboXS is made, and that there are flex joints in both pieces that make both installation easy and also greatly reduce any noise, vibration and harshness intruding into the cabin from the exhaust system. You can also do things to the rp section without the pain of removing or damagingthe dp, such as adding a reso (which I did) or installing a high flow cat, should you desire to do so, if you are running catless.
Not in any way criticising those who like the one piece setup, just pointing out that there are advantages to the two piece design that might not be obvious to those who have not installed and run the dp/rp in this manner.