the feathered / non-feathered may have the same tog value initially, but,
the feathered one, if looked after will give 10+ years of service and maintain its warmth versus the non-feathered where the insulation will degrade. - people I know are buying a non-feathered every couple of years.
I'm not sure I'd want to keep a duvet that long. Everyone sweats at night and duvet covers will only absorb so much before it gets through to the actual duvet.
Unless you've got a massive washing machine capable of washing it, I think I'd prefer to replace every few years.