It is astonishingly good stuff. A place I worked at once in London used to give out Harrod's vouchers at Christmas. I went to the food hall with mine and got the fanciest 'By appointment to Her Maj' haggis they had, for a pretty penny (but free to me). It was great, but to be honest no different from other supposedly humbler haggises (it somehow feels like the plural should be haggi).

It's the richness of the recipe that makes it, I think, rather than needing or even benefiting from fancier ingredients.