Belts, sparkplugs, leads etc I use oem parts, oven the Audis air-filter is a k&n not the manufacturer one.
That said, the Oil filter is a genuine part, the oil is the higest quality stuff I can get on the basis that if these parts fail or dont perform, I have to go and get another engine built.
I think its fair enough on non critical parts but having lost a cam-belt on a classic car because it was a counterfit part from a Halfords type place I would never use anything this vital that isnt main dealer or a premium part.
in my case, its another £50 on an oil and filter change or £2000 for a re-engine