The reason why they claim the extra response is due to increase thermal efficiency by keeping more energy (heat) in the turbine housing. However they usually lead to housing prematurely failing due to heat stress (cracking) as the heat struggles to escape. It does help response to a certain degree but once the turbo is up to temperature it makes no difference as the heat is already there, and anyone who has had a turbo bright red will know how long they take to stop glowing! Extra horse power is bullshit though.