My fiancee has never told me directly to quit using concealer (used to be Toppik, now Prothik). However, she has made it clear that she's not crazy about it. She prefers my hair "as-is", which I did for some time until the thinning got to a point where I actually looked bald, as opposed to just thinning.
Her main complaints:
-can't run her hands through my hair
-discolors my hair (she loves my natural color)
-I'm always worrying about how it looks (which I do with or without concealer)
-I can't leave my hair out of a ponytail with concealer
-It looks dull and dusty at times
She wasn't crazy about me wearing a hairpiece at first, either, though she quickly came around. She likes that it's actually touchable hair again, as opposed to the stiffness of all the product I used to fix the Prothik. (for the record, I still use Prothik behind my partial, but it's appearance is minimized by the hair of the piece, given that I wear it in a ponytail and I don't use as much product, since I don't have to use Prothik right at the hairline anymore)