The HKS worked perfectly fine on my '02 WRX but at the time there wasn't many budget minded alternatives. The flat flange honestly works fine with the stock TD04 and smallish turbos. The HKS still looked like-new after one year on my car.

I did have the Helix V2 downpipe on my '04 STi. The fitment wasn't 100% perfect but overall it was a nicer downpipe compared to the HKS.