For one, it's OEM some people like the idea of everything on their car being from manufacturer. But the k04 is also very reliable whereas quite alot of people have had reliability issues with their k03 hybrid. In fact if Im not mistaken CR Turbos has a long list of lawsuits against them from less than happy customers. I've known a few members myself who have gone through 2 CR Turbo hybrid k03 turbos in under 3 months. Each time they would blame 'oil contamination' as the reason for turbo failure...
But also for those that trust in hybrid turbos and want more power than a k03 can give but don't want to go for a big turbo setup they can send a k04-02x unit off to fit a k06 compressor wheel inside which gives around 320bhp
