Taking cost vs. benefit into account, I would default to "no". This one in particular seems like a "neat little feature", but "neat" does not cut it if it threatens to make legislation against surveillance-based advertising less effective.

I'm not sure many customers will miss it, if they really notice. Yes it can be a bit helpful, but many other things in the world would be "a bit helpful" and yet are nowhere near justifying their cost and effect (e.g. we stopped using radioactive chemicals in substantial amounts for everyday products very, very quickly).