Its something i havnt used but the way i see it is...
If your line breaks, there is nothing holding the tubing to the lead unlike other set ups, so the tubing will simple slide of the line, then there will be no tension and the rig wouldnt be able to be pulled off the tubing, leaving rig and tube attached to the fish, it might be the safest rig, it might just be the way im looking at the situation
I have noticed that Fox do a tubing heli pack though.
Im going to have to go and have a play me thinks