Smaller diameter silicone doesnt collapse as easy when flexed or bent, due to the wall size in ratio to the hole size, whilst big stuff like 15mm+ will collapse round tight bends and cause issues. Plus the VW stuff has smaller and less flexible walls than the vacuum silicone, I'd go the silicone route, thicker walls, better under heat easy to route as I have done it on my engine (no plastic used, even, no tight bends that could cause the silicon to collapse at all), plus due to the hose thickness you can re-use the standard plier clips, plstic mount clips and T-piece. Only thing that is really stiff is the fuel line to the rail which requires special piping due to the fuel involvement.
