I've thought about these off an on for a year or so. Not sure if this offers much in the way of an improvement over the front maifold, however it does offer an opportunity to replace the restrictive "Y" cast into the rear manifold, and perhaps to create a true 3" downpipe and catback.
The question is: is there sufficient room near the firewall to have a custom 3" "Y" fabricated to connect the downpipe, rear manifold and new crossover tube?
Not sure I want to be the one to spend the money to find out - I'm already into the LS6 intake swap for ~$500.