The one thing I like most about this system is the fact that the header tubes are hydroformed and seamless, it appears that the header assy, 3 into 1 collector, what appears to be a cat convertor and the S bend are all welded as one piece, I certainly hope that their assy/welding jig was true and correct.
Most exhausts will perform better with a reflashed ECU. Even the akrapovic titanium which is advertised to work great with the stock tune runs better after flashing the ECU... So to answer the question, you probably don't "need" to flash it, but it will almost definitely run better if you do.
From the photo I posted at the top I see the balance tubes between the headers, in the photo of the exhaust out of the box, I do not see the balance tubes between the headers, JDM197, would you elaborate on this, are there balance tubes between your headers on the production model, a photo would be nice to see