A genuine VVT adjuster is knocking on the doors of £400 on it's own, so the fact the whole ebay shebang costs £239 ought to tell you something.
As above, genuine only for critical engine components.
VVT sprockets only need replacing if the oil control rings have worn deep grooves into the centre bore, which will cause lazy VVT advance/retard, or if it gets messed up when removing the Polydrive bolt.
Early engines had metal oil control rings which caused said wear grooves. Later engines switched to plastic rings which don't eat into the metal so much. No need to spend 400 quid + chain gear if it's not necessary.
