Yes, it is 'supposed to give you a freer flowing exhaust that'll decrease spool up time and increase power and torque !
Imho, you'd be better off getting a 3" Janspeed elbow and downpipe. I've never seen the point of putting a large bore downpipe and system on the back of the OE elbow with it's small diameter exit......I guess that's just me though !
Just a heads up, the HKS pipe is made from mild steel so, might only last you 2 years or so. If you're determined to go down that route, it'll be better and cheaper most likely, to get a stainless downpipe fabricated at a Powerflow place or similar !