I hate the word "frumpy". It's completely subjective.
I don't really see the point of threads like this. You (general you) have seen something you like so why do you need the validation of a bunch of random internet posters? If you do, then you probably don't like the item enough in the first place.
If you're asking the same random bunch of posters if it's "mumsy" or "on trend" or "dated", don't you think the design team at brands like Cos (especially Cos) or Massimo Dutti might be a bit more reliable and knowledgeable than the random posters on here?
Comments like housethatbuiltme's explaining why she doesn't like the Cos boots, but without trying to set herself up as some sort of style expert are, I think the most helpful. "Mumsy" "frumpy" aren't in the least bit helpful.