A sequential blow off valve will not open at any BOOST pressure , it will only open when lifting off the throttle , sequential is the HKS design of valve , there r 2 valves which r sequential in operation.
Sequential blow off valves and dump valves perform the same function but the HKS sequential is a more elaborate and efficient design.
Your car has a recirculating dump valve anyway , but an aftermarket valve will b more robust and won't leak boost pressure especially when boost is raised.
Dump valves which blow to the atmosphere will probably invalidate warranty due 2 controversy that they can damage engines , which in the case of the HKS sequential is rubbish , mine has been installed for about 10k miles with no problems.