Just priced up for what my child needs, worked out as £130ish from M&S, and £66 from Asda George.
However if the Asda falls apart after a few months and we buy twice it will end up the same cost. But maybe it’s hard wearing?
I really don’t have any family with kids or any friends with school aged kids to ask!
YABU - Asda (or other supermarkets) are just as good
YANBU - M&S Uniform is worth the cost