When I went looking for chocolate sandwich biscuits (Prinzen-Rolle), I saw that the store-brand version was larger and cost less.
The "cost per kg" in the small print on the label helpfully told me that the store-brand biscuits cost pretty much exactly half of what the Real Thing cost. So I thought I'd try them.
Store-brand chocolate sandwich biscuits tend to have more sugar in them than I like, but the ingredient lists on the two products seemed similar enough so I thought I'd give them a try; the Prinzen-Rolle would, after all, still be there in case the store-brand ones turned out to be not that great.
Well, a couple of biscuits later, I think I should have gone with the Prinzen-Rolle.
The filling hasn't got appreciably more sugar than the Prinzen-Rolle, so that's not the problem—but the biscuits just taste, somehow, "flat". Uninteresting. Crunchy cardboard. And I also remember the chocolate filling in the Prinzen-Rolle as being richer somehow.